Stabilizing properties of fucoidan for the alumina suspension containing the cationic surfactant

The paper presents the influence of fucoidan (FD) on stability of alumina suspensions in the presence of cationic surfactant hexadecyltrimethylammonium bromide (CTAB). The research results show that fucoidan adsorbs on the alumina surface and that the adsorption decreases in the CTAB presence.

Carbohydrate Polymers 245 (2020) 116523 Contents lists available at ScienceDirect Carbohydrate Polymers journal homepage: www.elsevier.com/locate/carbpol Stabilizing properties of fucoidan for the alumina suspension containing the cationic surfactant T Jakub Matusiaka,*, Elżbieta Grządkaa, Anna Bastrzykb a Department of Radiochemistry and Environmental Chemistry, Faculty of Chemistry, Institute of Chemical Sciences, Maria Curie-Sklodowska University, M CurieSklodowska Sq 3, 20-031 Lublin, Poland b Department of Process Engineering and Technology of Polymer and Carbon Materials, Faculty of Chemistry, Wroclaw University of Science and Technology, Wybrzeze Wyspianskiego 27, 50-370 Wrocław, Poland A R T I C LE I N FO A B S T R A C T Keywords: Adsorption Biopolymer Aluminium(III) oxide Interface Electrosteric Turbidimetry The paper presents the influence of fucoidan (FD) on stability of alumina suspensions in the presence of cationic surfactant hexadecyltrimethylammonium bromide (CTAB) The research results show that fucoidan adsorbs on the alumina surface and that the adsorption decreases in the CTAB presence This is due to formation of the polymer-surfactant complexes characterized by lower affinity for the alumina surface than pure fucoidan The complex formation was confirmed by the tensiometric studies where the increase of the CTAB/FD surface tension in comparison to pure CTAB was observed It was established that fucoidan possesses great stabilizing efficiency regardless of pH Furthermore, stability of the fucoidan/alumina system increased after CTAB addition due to the presence of non-adsorbed complexes between the alumina particles The results indicate that fucoidan could be successfully used as a stabilizer of colloidal suspensions where the presence of surfactant is required, that is in cosmetic and pharmaceutical industries Introduction stabilizing properties of the fucoidan/alumina system Therefore to get a full picture of the system stability a lot of measurements have to be conducted including the adsorption of the polymer on the solid surface, stability studies, determination of the interactions between the surfactant and the polymer, and the electrokinetic properties Multiple methods can be used to characterize the interactions between the polymer and the surfactants Among others, those are nuclear magnetic resonance spectroscopy (Grządka, Matusiak, & Stankevič, 2019), smallangle neutron and X-ray scattering (Penfold et al., 1997; Shtykova et al., 2000), isothermal titration calorimetry (Skvarnavičius, Dvareckas, Matulis, & Petrauskas, 2019) and surface tension measurements (Touhami, Rana, Neale, & Hornhof, 2001) In the case of the adsorption and stability such techniques as UV–vis, FT-IR (Chiem, Huynh, Ralston, & Beattie, 2006), QCM-D (Krasowska, Zawała, Bradshaw-Hajek, Ferri, & Beattie, 2018), ellipsometry (Fujiwara., 2007) and turbidimetry (Ostolska & Wiśniewska, 2014) are used Another factor influencing stability of colloidal systems is the conformation of adsorbed macromolecules added to the system Due to the complex interactions between the macromolecules and the solid surface, adsorbed polymer chains can be characterized by different configurations (Gregory & Barany, 2011) Such configuration has a direct influence on the stabilizing potential of used polymers When the polymer Induced stability is a vast subject in the case of different colloidal systems (Studart, Amstad, & Gauckler, 2007) Since such systems are not naturally stable, it is very important to increase their stability (Singh, Menchavez, Takai, Fuji, & Takahashi, 2005) In terms of industrial applications stability of a new product determines not only its sensory properties but also the economic value of the final product The consumer demands for organic, non-toxic and environmentally friendly products generate the urge to study new possible substances that can permanently replace their synthetic substitutes In the case of beauty, cosmetic, and pharmaceutical industries such seemingly basic research leads to the development of more sophisticated ones as well as to the whole new field of R&D The suspensions containing different oxides, stabilizers, bioactive substances, and surfactants are commonly used to care and treat human skin and health In such complicated systems, each component can interact with others changing the properties of the whole system This is of great significance to the interactions between the polymers (stabilizers) and the surfactants Such interactions influence not only the adsorption of the polymers on the oxide surface but also the long-time system stability Hence the authors infer that the presence of the cationic surfactant influences the adsorption and ⁎ Corresponding author E-mail addresses: jakub.matusiak@poczta.umcs.lublin.pl (J Matusiak), egrzadka@poczta.umcs.lublin.pl (E Grządka), anna.bastrzyk@pwr.edu.pl (A Bastrzyk) https://doi.org/10.1016/j.carbpol.2020.116523 Received 13 February 2020; Received in revised form 21 April 2020; Accepted 25 May 2020 Available online 03 June 2020 0144-8617/ © 2020 The Author(s) Published by Elsevier Ltd This is an open access article under the CC BY license (http://creativecommons.org/licenses/BY/4.0/) Carbohydrate Polymers 245 (2020) 116523 J Matusiak, et al pharmaceutical use concentration is low and the number of the active centres on the surface is not limited, the polymer chains usually form the flat configurations on the solid surface, where so called trains structures predominate Between two trains, segments called loops can be observed Loops are attached to the solid surface by trains, and most of their segments is present in the bulk phase At the end of each trains, a free chains extending towards the bulk of the solution can be observed They are called tails (Nylander, Samoshina, & Lindman, 2006) For small solid particles more extended configurations were observed, whereas for larger ones where the surface was not limited the flat trains conformation predominated (Chodanowski & Stoll, 2001) Moreover, with the increasing polymer concentration the configuration changes from the flat to the more extended one (Nylander et al., 2006) The conformation of the polymers on the solid surface can be also confirmed using the zeta potential measurements The formation of the extended adsorption layer containing numerous loops and tails leads to the decrease of the zeta potential (Ostolska & Wiśniewska, 2015) To confirm the Author’s hypothesis ternary system composed of aluminium(III) oxide acting as a solid substance, fucoidan as a polymeric stabilizer, and the cationic surfactant hexadecyltrimethylammonium bromide (CTAB) as a surface active agent was used Fucoidan is a natural sulfated polysaccharide present in different species of brown seaweeds Since its discovery by Kylin in 1913 (Kylin, 1913), it has been extensively studied for ages Just like in case of other marine polysaccharides both the composition and the structure vary according to the species, season, and harvest location of the plant According to Fletcher et al the basic structure of fucoidan is composed of sulfated fucose backbone, however, it can contain other sugars such as galactose, uronic acid and xylose (Fletcher, Biller, Ross, & Adams, 2017) Rioux et al observed that the molecular weight of fucoidan can also vary significantly from low molecular weight to high polymeric structures of 1600 kDa (Rioux, Turgeon, & Beaulieu, 2007) Fucoidan is a highly bioactive substance with potentially positive health effects such as anticancer, anticoagulant and antithrombotic, antivirus, antitumor and immunomodulatory activities (Zong, Cao, & Wang, 2012; Li, Lu, Wei, & Zhao, 2008; Ale, Mikkelsen, & Meyer, 2011) What is particularly important for skin care products is that fucoidan has also the antioxidant and anti-inflammatory properties (Li et al., 2008; Wijesekara, Pangestuti, & Kim, 2011; Wang, Zhang, Zhang, & Li, 2008) The non-clay materials such as mineral oxides are a group of ingredients used in cosmetic and pharmaceutical industry in such products as creams, emulsions, pastes etc (Carretero & Pozo, 2010; Morganti, 2010) Aluminium(III) oxide, also called alumina, is one of such materials used in cosmetic industry FDA (Food and Drug Administration) confirmed that alumina is a safe material for the use in contact with soft tissues, bones, and internal organs According to Becker et al alumina is used industrially in the leave-on products such as nail polish, around the eye cosmetics and skin care products (Becker et al., 2016) The lack of papers concerning the use of fucoidan as a stabilizer for different colloidal systems is observed The novelty proposed by the Authors is the use of natural stabilizer possessing potential health promoting properties This approach reduces the need for the use of other synthetic stabilizers and increases the product applicability The main goal of this study was to investigate the influence of fucoidan on stability of the alumina suspensions in the presence and absence of the cationic surfactant CTAB To characterize the types of stability of the fucoidan/CTAB/alumina systems the adsorption measurements (UV–vis, FT-IR) were conducted Stability of the studied systems was measured by means of the turbidimetric method using the TSI index Moreover, the influence of pH on the adsorption, stability and electrokinetic properties was also studied The obtained results indicate greatly stabilizing properties of fucoidan for the alumina suspensions in the presence and absence of the cationic surfactant and the whole studied pH range (3–7) which enables its use as an efficient stabilizer for the colloidal suspensions with the possible cosmetic and Materials and methods 2.1 Materials Fucoidan (Fucus serratus) sulfated L-fucose algal polysaccharide was obtained from Carbosynth Limited (CAS No 9072-19-9) Its chemical formula is (C6H9O3SO3)n The molecular weight of this compound declared by the manufacturer equals 705 000 Da However, this value was also verified using the static light scattering method (Zetasizer NanoZS, Malvern Instruments) In this technique the scattering intensity of a number of concentrations of the sample (2000−4000 ppm) was measured and used to construct the Debye plot created by measuring the scattered light at a single angle (173°) at multiple sample concentrations with water as a standard From this plot the average molecular weight (Mw) (obtained from the intersection point between the obtained Debye plot and the ordinate axis) and the second virial coefficient (A2) (determined from the slope of the Debye plot) were calculated According to the measurements the molecular weight of fucoidan equals 730 000 Da whereas the A2 coefficient 0.000321 cm3 mol g−2 Moreover, the content of sulfate groups in the fucoidan was estimated by means of the barium sulfate precipitation method using the barium chloride-gelatin reagent (Dodgson & Price, 1962) The exact procedure altogether with the calibration curve has been included in the Appendix A The sulfate content obtained with this method equalled 5.96 %, which agrees with the literature data (Lim & Mustapha, 2017) Hexadecyltrimethylammonium bromide is a cationic quaternary ammonium surfactant (CAS No 57-09-0) It was obtained from Fluka Analytical The chemical formula of this compound is CH3(CH2)15N(Br) (CH3)3 whereas its molecular weight equals 364.45 Da The concentration of the surfactant in all conducted measurements was 0.002 % Such concentration did not exceed the critical micelle concentration (CMC) of CTAB (0.00092 mol dm−3 = 0.0337 %) (Li, Zhang, Zhang, & Han, 2006) Aluminum oxide (Al2O3) (CAS No 1344-28-1) was used as the adsorbent The oxide was washed with doubly distilled water until its conductivity was lower than μS cm−1 The XRF measurements (Epsilon 5, PANalitycal) confirmed that the adsorbent is free of impurities and the studied sample contained over 99.6 % of Al2O3 In order to get full characteristics of the adsorbent the SEM images (Quanta 3D FEG, FEI), the low-temperature adsorption-desorption of nitrogen BET (ASAP 2420, Micromeritics Inc.) and the dynamic light scattering (Zetasizer Nano ZS, Malvern Instruments) methods were used The structure of measured alumina is presented in Fig The specific surface area of Al2O3 equals 171 m2/g, the adsorption average pore width equals 15.67 nm whereas the pore volume is 0.67 cm3/g The average particle size of alumina calculated by intensity equals 172.4 nm 2.2 Methods 2.2.1 Stability measurements The turbidimetric method is one of the most precise methods to determine stability of colloidal suspensions The methodology of stability measurements was previously described (Matusiak, Grządka, & Bastrzyk, 2018) 0.005 g of alumina was dispersed in 10 cm−3 of a solution containing NaCl (0.01 mol dm−3) The suspensions were treated by ultrasounds for 30 s In the case of the samples containing fucoidan (20−1000 ppm) and FD + CTAB (100 ppm + 0.002 %), the substances were added after the ultrasound treatment was applied pH of the suspensions was adjusted to using either the HCl or NaOH solutions 2.2.2 Adsorption measurements The amount of fucoidan adsorption on the Al2O3 surface was Carbohydrate Polymers 245 (2020) 116523 J Matusiak, et al cm–1 and the mirror velocity 2.5 kHz at room temperature using the Bio-Rad Excalibur FT-IR 3000 MX spectrometer and the MTEC Model 300 photoacoustic cell The cell was purged with dry helium prior to the measurements The spectra were normalized as MTEC carbon black was used as a standard The samples of fucoidan, alumina and fucoidan adsorbed on alumina were directly placed in a 10 mm stainless steel cup (sample thickness was lower than mm) For each spectrum the interferograms of 1024 scans were averaged Smoothing functions were not used All spectral measurements were performed at least three times 2.2.5 Electrokinetic properties The surface charge density and the point of zero charge (pHpzc) of alumina (0.1 g) in the presence and absence of fucoidan (200−800 ppm) and CTAB (0.002 %) was determined using the potentiometric titration method The background electrolyte used in this study was 0.01 mol dm−3 NaCl The measurements were conducted in a thermostated Teflon vessel with a shaker to which an automatic burette (Dosimat 665, Methrom) and a pH-meter were connected The whole process was controlled by the Titr_v3 computer program written by W Janusz The zeta potential of the alumina suspensions was calculated from the electrophoretic mobility measurements and the Smoluchowski equation (Zetasizer Nano ZS, Malvern Instruments) The sample of alumina (0.01 g) was added to 100 cm3 of the background electrolyte solution (NaCl, 0.01 mol dm−3) and treated with ultrasounds (3 min) Next in some systems fucoidan (1−100 ppm) or fucoidan (10 ppm) and CTAB (0.002 %) were added The obtained data are presented as the zeta potential curves versus pH Moreover, pHiep (the isoelectric point) was also estimated All measurements were performed five times and the average values are reported Fig SEM morphology of alumina; magnitude 100 000× calculated from the concentration difference before and after the adsorption measurements using a calibration curve The first step of the measurements was preparation of the polymer/electrolyte/metal oxide suspensions in the same systems additionally enriched by CTAB A portion of alumina (0.05 g) was added to 10 cm3 of solution containing fucoidan (the concentration range from 20 to 600 ppm), NaCl (0.01 mol dm−3), doubly-distilled water and in some systems CTAB (0.002 %) The pH of the obtained suspensions was adjusted to using HCl or NaOH, respectively (pH meter, Beckman φ 360) The suspensions were shaken for 18 h in the water bath at the temperature 25 °C, 120 rpm (OLS26, Grant) to achieve the adsorption-desorption equilibrium To determine the fucoidan adsorption on the alumina surface the spectrophotometric method was used (Albalasmeh, Berhe, & Ghezzehei, 2013) cm3 of H2SO4 (98 %) was added to cm3 of supernatant obtained after centrifugation of a suspension using a high-speed centrifuge (310b Mechanika Precyzyjna) The samples absorbance was measured at 315 nm with a UV–vis spectrophotometer (Cary 100, Varian Instruments) Doubly-distilled water was used as the reference All measurements were done four times and the average values are reported Results and discussion Adsorption of polysaccharides on the solid surface is a process governed by multiple factors among which pH, type and concentration of the used electrolyte as well as the presence of surfactants play a major role (Grządka & Matusiak, 2017; Grządka, Matusiak, & Paszkiewicz, 2018) One should be aware that while discussing the polymer adsorption on the oxide surface, the state of the solid surface is particularly important Since the number of the adsorption centres on the solid surface is constant, pH is the main parameter controlling the adsorption of the ionic polysaccharides on the metal oxide The protonation/deprotonation reactions taking place on the solid surface involve some changes in the concentration of the surface groups responsible for the interactions with the adsorbate For aluminium(III) oxide the isoelectric point is close to pH = which agrees with the literature data (Kosmulski, 2018) In such case alumina is positively charged at pH lower than pHiep and negatively charged above pH = Thus, the adsorption of anionic fucoidan below pHiep is most likely electrostatically driven (Liu, Zhang, & Laskowski, 2000) Fig represents the fucoidan adsorption on the alumina surface depending on suspension pH As one can see, the fucoidan adsorption on Al2O3 is the highest at the acidic pH (high concentration of the positively charged surface groups), but it decreases with the increasing pH This is a result of the electrostatic interactions between the negatively charged polymer groups and the positively charged solid surface groups These interactions are the strongest at low pH values Since the concentration of the sulfate groups present in the polymer chain is not high, besides for the electrostatic interactions most likely the hydrogen bonding and hydrophobic interactions take place in the adsorption mechanism (Merta, Tammelin, & Stenius, 2004) The studies presented by Indest et al showed that the ionic strength influences the adsorption of fucoidan on PET-chitosan films (Indest et al., 2009) This is in agreement with the general opinion that the adsorption of the ionic polymers increases with 2.2.3 Surface tension measurements To analyze the interactions between fucoidan and CTAB the surface tension measurements of the surfactant without any additives as well as in the presence of fucoidan were conducted (Theta Optical Tensiometer, KSV Instruments) The pendant-drop method was used to estimate the critical micelle concentration of pure CTAB as well as the critical association concentrations of this cationic surfactant in the presence of fucoidan (200 ppm) The analysis of the obtained data is based on fitting the equations to drop profiles for the pendant drop using the Young-Laplace equation: 1⎞ Δp = γ ⎛ + R2 ⎠ ⎝ R1 ⎜ ⎟ (1) where: Δp (Pa) is the difference in pressures of the fluids across the interface, γ (N/m) is the interfacial tension of the fluid pair, and R1 and R2 (m) are the radii of curvature of the interface in the orthogonal directions All measurements were made at least five times and the average values are reported 2.2.4 FT-IR spectroscopy FT-IR/PAS spectroscopy was used as the complementary technique for confirmation of fucoidan adsorption on the alumina surface The spectra were collected in the 4000−400 cm–1 range with the resolution Carbohydrate Polymers 245 (2020) 116523 J Matusiak, et al Fig The influence of pH on fucoidan adsorption (200 ppm) on the alumina surface; 0.01 mol dm−3 NaCl Fig The FT-IR/PAS spectra of (a) fucoidan (FD), (b) post-adsorption and (c) pre-adsorption alumina Comparing the spectra before and after adsorption, it is clear that fucoidan adsorbs on the alumina surface At 2950−2850 cm−1 and 1415 cm−1 the C–H stretching vibrations can be observed Clearly visible in the FD spectrum (Fig 4a) and slightly covered by the eOH vibrations (1640 cm−1) (Fig 4b) a band attributed to the stretching of dissociated carboxylic group COO− (1609 cm−1) can be observed This band indicates that uronic acid is present in the fucoidan chain which is in agreement with the literature data (Marinval et al., 2016) At 1148 and 1077 cm−1 the bands responsible for the C–O stretching vibrations are visible, whereas at 1746 cm-1 stretching of C]O is observed However, one should keep in mind that the absorption band of the carbonyl group is one of the strongest known in IR spectroscopy (Socrates, 2001) Thus, the band intensity is not strictly correlated with the concentration of the C]O groups The bands unique for fucoidan visible at 1234–1251 and 819–850 cm–1 corresponds to the S]O asymmetric stretching vibrations of sulfate groups and C–O–S vibrations, respectively (Chale-Dzul, Moo-Puc, Robledo, & Freile-Pelegrín, 2015; Wang et al., 2010; Shanura Fernando et al., 2017) One of the most common methods used to study the interactions between surfactants and polymers is the measurement of surface tension It can be observed that the surface tension in the CTAB/FD system increases in comparison to the pure CTAB solution (Fig 5) Such observation indicates the presence of interactions between the polymer and the surfactant There are several points on the surface tension isotherm of surfactant solution that can be observed after the addition of the polymer The critical association concentration (T1, CAC) is observed when the interactions between the surfactant and the polymer start In this region the CTAB molecules start to bind to the FD chains, resulting in the formation of polymer-surfactant complexes (Bit, Ali, Debnath, & Saha, 2010) Considering the fact that CAC is always lower than the critical micelle concentration (CMC) (Thalberg, Lindman, & Karlström, 1990), in the CTAB/FD system the interactions start at a very low surfactant concentration, indicating non-cooperative Fig The influence of the cationic surfactant CTAB on the fucoidan (FD) adsorption on the alumina surface; pH = 7, 0.01 mol dm−3 NaCl the increasing salt concentration or ionic strength (Chibowski, OpalaMazur, & Patkowski, 2005) The ionic strength used in the following measurements (IS = 0.01 NaCl) is low, so it doesn’t have a high influence on the fucoidan conformation on the alumina surface To discuss the conformation of fucoidan on the alumina surface, different factors must be examined The used adsorbent is nano-alumina with the mean particle size of 172.4 nm The studies of Chodanowski pointed out that in case of small solid particles, more extended configuration of the polymer is observed (Chodanowski & Stoll, 2001) This agrees with the presented adsorption data It can be observed that the adsorption increases steadily with the increasing concentration, whereas the plateau is not reached (Fig 3) Considering the fact, that the polymer is unable to adsorb at the inner pores of alumina, the most probable structure of the adsorbed fucoidan layer is the conformation rich in loops and tails, rather than flat trains The presence of cationic surfactant also influences the polymers adsorption on the solid surface The interactions between those molecules can lead to the formation of polymer-surfactant complexes In such case the polymer adsorption in the presence of the surfactant can either increase or decrease There are a few explanations for this phenomenon If the surfactant interacts with the polymer resulting in the formation of complexes, and such complexes are more likely to remain in the bulk of the solution, the lower adsorption is observed (Fig 3) In this case some of the fucoidan macromolecules interact with the CTAB molecules resulting in the formation of non-adsorbing complexes The adsorption decrease is due to the fact that fewer fucoidan chains are adsorbed on the alumina surface and thus the adsorption is smaller On the contrary if the surfactant is not present in the system, the free polymer chains can only interact with the surface which results in a higher adsorption FT-IR/PAS spectroscopy was used as a complementary method to confirm the fucoidan (FD) adsorption on the alumina surface Fig shows the spectra of pure FD, post-adsorption, and pre-adsorption alumina Fig The changes of CTAB surface tension in the presence of fucoidan (FD, 200 ppm); T = 25 °C Carbohydrate Polymers 245 (2020) 116523 J Matusiak, et al binding of surfactant molecules to the polymer chain (Khan & Brettmann, 2015) When the polymer chains become saturated with the surfactant molecules, the critical saturation concentration point (T2) can be observed However, sometimes this point is hard to quantify experimentally A further increase of the surfactant concentration leads to the situation where the polymer chain is saturated and it is more thermodynamically favourable for the surfactant to form micelles (Goddard, 1986) It is known that the polymer and the surfactant will interact in solutions, mostly by hydrophilic, hydrophobic and electrostatic interactions The association between the surfactant head groups and the polyelectrolytes is driven by the entropic gains whereas enthalpic contributions should be also mentioned (Bai, Santos, Nichifor, Lopes, & Bastos, 2004) In the case of the CTAB/FD system the electrostatic interactions are most likely responsible for the initial contact because of the strength of the electrostatic forces whereas the hydrophobic effect occurs in the micelle formation stage (Khan & Brettmann, 2015) The end of the interactions between CTAB and FD can be observed in the final stage of the surface tension isotherm A system is considered stable when the sum of the repulsion forces is equal to the attractive ones Keeping that in mind there are different factors influencing stability of the colloidal systems, among which pH and the presence of other molecules can be mentioned Fig 6a shows the influence of the fucoidan concentration on stability of the alumina suspensions The TSI values change from to 100 being the lowest for the most stable and the highest for the completely unstable systems As one can see, the alumina suspension itself is rather unstable (change of TSI from 9.64 in the first hour to 68.75 in the fifteenth hour) The reason for this is the low efficiency of the electrostatic mechanism responsible for stabilization of “hard” colloidal particles When two particles contact, their electrical double layers overlap which results in the repulsion of solid particles However, the efficiency of such mechanism decreases in time when particles aggregate and destabilization occurs (Tadsors, 2012) The addition of the adsorbing anionic polymer clearly influences the system stability It can be observed that stability increases greatly with the concentration Such situation occurs when the oppositely charged polymer chains adsorb on the solid surface, creating a compact layer of macromolecules This process is called electrosteric stabilization for ionic polymers and steric stabilization for non-ionic ones At pH = the alumina surface is still positively charged whereas the fucoidan chains possess the anionic charge in terms of sulfate (–O–SO3−) and carboxyl dissociated groups (–C–O–O−) This leads to the formation of the fucoidan layer, increasing the output of the repulsive forces in the system The largest system stability is observed for the concentration of fucoidan equal 1000 ppm In this case TSI increases from 2.89 in the first hour to 26.43 in the fifteenth hour For the alumina suspensions without the polymer the difference in TSI from the first to the last measurements is 59.11 whereas for the alumina/fucoidan 1000 ppm system it is only 23.54 As pH has a great effect on the protonation/ deprotonation reactions on the solid surface, its influence the fucoidan/ alumina system stability was also studied (Fig 6b) As follows from the measurements pH has an insignificant effect on the fucoidan/alumina system stability This is consistent with the adsorption data that the highest stability is observed at pH = where the alumina surface possesses the largest positive charge and fucoidan adsorption is the highest Stability decreases slightly with the increase of pH due to the formation of less packed polymer adsorption layer The final factor influencing the fucoidan/alumina system stability is the presence of the cationic surfactant CTAB (Fig 6c) The presence of CTAB increases the stabilization efficiency of fucoidan for the alumina suspension As indicated by the adsorption and surface tension data (Figs and 5) fucoidan forms complexes with CTAB characterized by lower affinity for the alumina surface than pure fucoidan Even though the adsorption layer in the presence of CTAB is less packed, the stability increase is still observed This is because the formed FD-CTAB complexes stabilize the alumina particles by orientating between them, Fig The influence of the fucoidan concentration (a), pH (b), and CTAB (c) on stability of the alumina suspensions The used conditions: pH = 7, 0.01 mol dm−3 NaCl (a); 100 ppm FD, 0.01 mol dm−3 NaCl (b); pH = 7, 0.002 % CTAB, 0.01 mol dm−3 NaCl (c) which results in the reduced attraction Fig 7a presents the influence of fucoidan concentration and Fig 7b the presence of CTAB on the zeta potential of the alumina suspension in the presence of 0.01 mol dm−3 NaCl as a background electrolyte As can be seen the alumina surface is positively charged up to pH = and starts to be negative above this value This indicates that the isoelectric point (pHiep) of this oxide is located near pH = 9, being consistent with the literature data (Kosmulski, 2001) However, the presence of negatively charged fucoidan causes the decrease of the zeta potential as well as the shift of the pHiep towards lower pH values There are a few reasons for this effect One is an anionic character of this polysaccharide Negatively charged groups from the fucoidan macromolecules present in the diffused part of the electric double layer cause the observed decrease Taking into account the fact that the electrokinetic mobility recalculated to the zeta potential is measured on the slipping plane, the shift of this plane towards the bulk solution caused by the fucoidan adsorption is also responsible for the zeta potential decrease Another observation from Fig 7a is that the higher concentrations of fucoidan are, the larger decrease is observed This is a consequence of higher fucoidan adsorption on the alumina surface occurring at higher concentration of this polysaccharide as well as a larger Carbohydrate Polymers 245 (2020) 116523 J Matusiak, et al Fig The Influence of fucoidan (FD) concentration (a) and the presence of CTAB (0.002 %) (b) on the zeta potential of alumina; 0.01 mol dm−3 NaCl Fig The Influence of fucoidan (FD) concentration (a) and the presence of CTAB (0.002 %) (b) on the surface charge of alumina; 0.01 mol dm−3 NaCl background electrolyte The first observation from the obtained data is that pHpzc for pure alumina is situated near pH = 8.5 which indicates that below this value the number of positively charged surface groups is the largest, whereas above this point the concentration of negatively charged groups is dominant This phenomenon changes a little bit after the addition of anionic fucoidan When the adsorption of polyanion occurs, the presence of negatively charged groups originating from the polysaccharide dissociation are present in the compact part of the electrical double layer Their presence causes the decrease in the surface charge density The higher the fucoidan concentration, the lower the values of the surface charge density are Another very important conclusion from Fig 8b is that the presence of cationic CTAB has an insignificant effect on the value of the surface charge density of the alumina/fucoidan system As follows the CTAB molecules not occur in large numbers in the compact part of the electric double layer but they are present in the upper, diffused layer, being consistent with the previous findings (Matusiak, Grządka, Paszkiewicz, & Patkowski, 2019) number of negatively charged groups present in the diffused part of the electrical double layer Moreover, the decrease of the zeta potential in the system containing the polymer in comparison to the system without it can be also attributed to the conformation of fucoidan on the alumina surface The adsorption measurements indicate that the adsorbed fucoidan chains are extending towards the bulk solution, rather than forming the flat adsorption layer With the increasing concentration the adsorption increases, whereas the zeta potential decreases (Fig 7a) The shift of the slipping plane towards the bulk solution can be caused by the conformation of adsorbed fucoidan For flat conformation lower decrease of zeta potential would be observed The zeta potential decreases greatly when the fucoidan concentration increases slightly, only from ppm to 10 ppm This can be attributed to the increasing number of the negatively charged fucoidan groups in the diffused part of the electrical double layer However, keeping in mind the adsorption measurements it can be assumed that the formed adsorption layer is rich in loops and tails structures, which results in the shift of the slipping plane and decrease of the zeta potential Fig 7b presents the influence of CTAB on the zeta potential of the 10 ppm fucoidan/alumina system This is clearly visible that the addition of the cationic surfactant causes the increase of the zeta potential values compared to the system without CTAB As follows the present cationic groups of the surface active agent have so large influence on the zeta potential that despite an obvious shift of the slipping plane accompanying the fucoidan adsorption on alumina in the presence of CTAB, the zeta potential increase takes place The electrokinetic properties of the compact part of the electric double layer can be analysed by means of the surface charge density measurements Fig 8a presents the effect of fucoidan concentration and Fig 8b the presence of CTAB on the surface charge density of the alumina suspension in the presence of 0.01 mol dm-3 NaCl as a Conclusions The presented study confirms high stabilizing properties of fucoidan for the alumina suspensions in all studied pH range According to the authors’ best knowledge the lack of such studies on the use of fucoidan as a stabilizer of colloidal suspensions is observed Thus, the obtained results are innovative and very promising in the field of colloidal stability and the use of natural polysaccharides in this field The adsorption and zeta potential studies allowed to establish that the adsorbed fucoidan layer is probably composed of extended structures, such as loops and tails The surface tension measurements confirmed the electrostatic complex formation between fucoidan and CTAB surfactant Carbohydrate Polymers 245 (2020) 116523 J Matusiak, et al Moreover, it was found out that in the presence of CTAB stability of the fucoidan/alumina system slightly increased due to the formation of non-adsorbed polymer-surfactant complexes orienting between the solid particles, which resulted in lower attraction and slower aggregation The results throw new light on the use of fucoidan as a natural stabilizer of the colloidal suspensions, particularly in the cosmetic and pharmaceutical industries Grządka, E., Matusiak, J., & Paszkiewicz, M (2018) Factors influencing the stability of the 2-hydroxyethyl cellulose/alumina system Cellulose, 25, 2839–2847 Grządka, E., Matusiak, J., & Stankevič, M (2019) Interactions between fluorocarbon surfactants and polysaccharides Journal of Molecular Liquids, 283, 81–90 Indest, T., Laine, J., Johansson, L.-S., Stana-Kleinschek, K., Strant, S., Dworczak, R., et al (2009) Adsorption of fucoidan and chitosan sulfate on chitosan modified PET films monitored by QCM-D Biomacromolecules, 10, 630–637 Khan, N., & Brettmann, B (2015) Intermolecular interactions in Polyelectrolyte and surfactant complexes in solution Polymers, 11, 51 Kosmulski, M (2001) Chemical properties of material surfaces New York: Marcel Dekker Inc Kosmulski, M (2018) The pH dependent surface charging and points of zero charge VII Update Advances in Colloid and Interface Science, 251, 115–138 Krasowska, M., Zawała, J., Bradshaw-Hajek, B H., Ferri, J K., & Beattie, D A (2018) Interfacial characterisation for flotation: 1.SOlid-liquid interface Current Opinion in Colloid & Interface Science, 37, 61–73 Kylin, H (1913) Biochemistry of sea algae Zeitschrift für physiologische Chemie, 83, 171–197 Li, B., Lu, F., Wei, X., & Zhao, R (2008) Fucoidan: Structure and bioactivity Molecules, 13, 1671–1695 Li, W., Zhang, M., Zhang, J., & Han, Y (2006) Self-assembly of cetyltrimethylammonium bromide in ethanol-water mixtures Frontiers of Chemistry in China, 1, 438–442 Lim, S J., & Mustapha, W A W (2017) Extraction of sulfated polysaccharides (fucoidan) from brown seaweed In J Venkatesan, S Anil, & S.-K Kim (Eds.) Seaweed polysaccharides 1st edition isolation, biological and biomedical applications (pp 27–46) Amsterdam: Elsevier Liu, Q., Zhang, Y., & Laskowski, J S (2000) The adsorption of polysaccharides onto mineral surfaces: An acid/base interaction International Journal of Mineral Processing, 60, 229–245 Marinval, N., Saboural, P., Haddad, O., Maire, M., Bassand, K., Geinguenaud, F., et al (2016) Identification of a pro-angiogenic potential and cellular uptake mechanism of a LMW highly sulfated fraction of fucoidan from Ascophyllum nodosum Marine Drugs, 14, 185 Matusiak, J., Grządka, E., & Bastrzyk, A (2018) Stability, adsorption and electrokinetic properties of the chitosan/silica system Colloids and Surfaces A, 554, 245–252 Matusiak, J., Grządka, E., Paszkiewicz, M., & Patkowski, J (2019) Complexes of fluorinated, silicone and hydrocarbon surfactants with carboxymethylcellulose and their influence on properties of the alumina suspension Colloid and Polymer Science, 297, 677–687 Merta, J., Tammelin, T., & Stenius, P (2004) Adsorption of complexes formed by cationic starch and anionic surfactants on quartz studied by QCM-D Colloids and Surfaces A, 250, 103–114 Morganti, P (2010) Use and potential of nanotechnology in cosmetic dermatology Clinical, Cosmetic and Investigational Dermatology, 3, 5–13 Nylander, T., Samoshina, Y., & Lindman, B (2006) Formation of polyelectrolyte–surfactant complexes on surfaces Advances in Colloid and Interface Science, 123–126, 105–123 Ostolska, I., & Wiśniewska, M (2014) Application of the zeta potential measurements to explanation of colloidal Cr2O3 stability mechanism in the presence of the ionic polyamino acids Colloid and Polymer Science, 292, 2453–2464 Ostolska, I., & Wiśniewska, M (2015) The impact of polymer structure on the adsorption of ionic polyamino acid homopolymers and their diblock copolymers on colloidal chromium(III) oxide RSC Advances, 5, 28505–28514 Penfold, J., Staples, E., Tucker, I., Creeth, A., Hines, J., Thompson, L., et al (1997) The composition of mixed surfactants and cationic polymer/surfactant mixtures adsorbed at the air-water interface Colloids and Surfaces A, 128, 107–117 Rioux, L.-E., Turgeon, S L., & Beaulieu, M (2007) Characterization of polysaccharides extracted from brown seaweeds Carbohydrate Polymers, 69, 530–537 Shanura Fernando, P., Asanka Sanjeewa, K K., Samarakoon, K W., Lee, W W., Kim, H.S., Kim, E.-A., et al (2017) FTIR characterization and antioxidant activity of watersoluble crude polysaccharides of Sri Lankan marine algae Algae, 32, 75–86 Shtykova, E., Dembo, A., Makhaeva, E., Khokhlov, A., Evmenenko, G., & Reynaers, H (2000) SAXS study of ι-carrageenan−surfactant complexes Langmuir, 16, 5284–5288 Singh, B P., Menchavez, R., Takai, Ch., Fuji, M., & Takahashi, M (2005) Stability of dispersions of colloidal alumina particles in aqueous suspensions Journal of Colloid and Interface Science, 291, 181–186 Skvarnavičius, G., Dvareckas, D., Matulis, D., & Petrauskas, V (2019) Thermodynamics of interactions between charged surfactants and ionic poly(amino acids) by isothermal titration calorimetry ACS Omega, 4, 17527–17535 Socrates, G (2001) Infrared and Raman characteristic group frequencies (3rd ed.) Chichester: John Wiley & Sons, Ltd Studart, A R., Amstad, E., & Gauckler, L J (2007) Colloidal stabilization of nanoparticles in concentrated suspensions Langmuir, 23, 1081–1090 Tadsors, T (2012) Electrostatic and steric stabilization of colloidal dispersions In H Oshima (Ed.) Electrical phenomena at interfaces and biointerfaces: Fundamentals and applications in nano-, bio-, and environmental sciences (pp 153–172) (first edition) Hoboken: John Wiley & Sons, Inc Thalberg, K., Lindman, B., & Karlström, G J (1990) Time-resolved fluorescence and selfdiffusion studies in systems of a cationic surfactant and an anionic polyelectrolyte Physical Chemistry, 94, 4289 Touhami, Y., Rana, D., Neale, G H., & Hornhof, V (2001) Study of polymer-surfactant interactions via surface tension measurements Colloid and Polymer Science, 297, 297–300 Wang, J., Zhang, Q., Zhang, Z., & Li, Z (2008) Antioxidant activity of sulfated polysaccharide fractions extracted from Laminaria japonica International Journal of CRediT authorship contribution statement Jakub Matusiak: Funding acquisition, Project administration, Conceptualization, Resources, Methodology, Investigation, Data curation, Visualization, Formal analysis, Writing - original draft, Writing review & editing Elżbieta Grządka: Supervision, Conceptualization, Methodology, Investigation, Writing - review & editing Anna Bastrzyk: Investigation, Resources Acknowledgements The Authors would like to acknowledge that this research was financially funded by the National Science Centre, Poland [grant number 2017/27/N/ST4/02259] Moreover, the work was supported by subsidy from the Polish Ministry of Science and Higher Education for the Faculty of Chemistry of Wroclaw University of Science and Technology Appendix A Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.carbpol.2020.116523 References Albalasmeh, A A., Berhe, A A., & Ghezzehei, T A (2013) A new method for rapid determination of carbohydrate and total carbon concentrations using UV spectrophotometry Carbohydrate Polymers, 97, 253–261 Ale, M T., Mikkelsen, J D., & Meyer, A S (2011) Important determinants for fucoidan bioactivity: A critical review of structure-function relations and extraction methods for fucose-containing sulfated polysaccharides from brown seaweeds Marine Drugs, 9, 2106–2130 Bai, G., Santos, L M N B F., Nichifor, M., Lopes, A., & Bastos, M (2004) Thermodynamics of the interaction between a hydrophobically modified polyelectrolyte and sodium dodecyl sulfate in aqueous solution The Journal of Physical Chemistry B, 108, 405–413 Becker, L C., Boyer, I., Bergfeld, W F., Belsito, D V., Hill, R A., Klaassen, C D., et al (2016) Safety assessment of alumina and aluminum hydroxide as used in cosmetics International Journal of Toxicology, 35, 16S–33S Bit, G., Ali, M., Debnath, B., & Saha, S K (2010) Solution properties of a polymernonionic surfactant mixed system Journal of Dispersion Science and Technology, 31, 1085–1090 Carretero, M I., & Pozo, M (2010) Clay and non-clay minerals in the pharmaceutical and cosmetic industries Part II Active ingredients Applied Clay Science, 47, 171–181 Chale-Dzul, J., Moo-Puc, R., Robledo, D., & Freile-Pelegrín, Y (2015) Hepatoprotective effect of the fucoidan from the brown seaweed Turbinaria tricostata Journal of Applied Phycology, 27, 2123–2135 Chibowski, S., Opala-Mazur, E., & Patkowski, J (2005) Adsorption of commercial, filtrated and fractionated polyethylene oxide onto hematite Materials Chemistry and Physics, 92, 519–525 Chiem, L T., Huynh, L., Ralston, J., & Beattie, D A (2006) An in situ ATR–FTIR study of polyacrylamide adsorption at the talc surface Journal of Colloid and Interface Science, 297, 54–61 Chodanowski, P., & Stoll, S (2001) Polyelectrolyte adsorption on charged particles: Ionic concentration and particle size effects-A Monte Carlo approach The Journal of Chemical Physics, 115, 4951–4960 Dodgson, K S., & Price, R G (1962) A note on the determination of the ester sulphate content of sulphated polysaccharides The Biochemical Journal, 84, 106–110 Fletcher, H R., Biller, P., Ross, A B., & Adams, J M M (2017) The seasonal variation of fucoidan within three species of brown macroalgae Algal Research, 22, 79–86 Fujiwara, H (2007) Spectroscopic ellipsometry: Principles and applications Chichester: John Wiley & Sons, Ltd Goddard, E D (1986) Polymer-surfactant interaction part II Polymer and surfactant of opposite charge Colloids and Surfaces, 19, 301–329 Gregory, J., & Barany, S (2011) Adsorption and flocculation by polymers and polymer mixtures Advances in Colloid and Interface Science, 169, 1–12 Grządka, E., & Matusiak, J (2017) The effect of ionic and non-ionic surfactants and pH on the stability, adsorption and electrokinetic properties of the alginic acid/alumina system Carbohydrate Polymers, 175, 192–198 Carbohydrate Polymers 245 (2020) 116523 J Matusiak, et al health benefits of sulfated polysaccharides derived from marine algae Carbohydrate Polymers, 84, 14–21 Zong, A., Cao, H., & Wang, F (2012) Anticancer polysaccharides from natural resources: A review of recent research Carbohydrate Polymers, 90, 1395–1410 Biological Macromolecules, 42, 127–132 Wang, J L., Guo, H Y., Zhang, J., Wang, X F., Zhao, B T., Yao, J., et al (2010) Sulfated modification, characterization and structure-antioxidant relationships of Artemisia sphaerocephala Carbohydrate Polymers, 81, 897–905 Wijesekara, I., Pangestuti, R., & Kim, S.-K (2011) Biological activities and potential ... need for the use of other synthetic stabilizers and increases the product applicability The main goal of this study was to investigate the influence of fucoidan on stability of the alumina suspensions... was also studied The obtained results indicate greatly stabilizing properties of fucoidan for the alumina suspensions in the presence and absence of the cationic surfactant and the whole studied... stability is the presence of the cationic surfactant CTAB (Fig 6c) The presence of CTAB increases the stabilization efficiency of fucoidan for the alumina suspension As indicated by the adsorption