Modification of the air–water interface by a chitosan adsorption process. Effect on an amphiphilic polymer monolayer

Monolayer formation by poly[(maleic anhydride)‐alt‐(stearyl methacrylate)] (MA‐alt‐StM) on aqueous subphases, with and without chitosan, was studied by the Langmuir technique. Chitosan (CS) modified considerably the shape of the MA‐alt‐StM isotherms on water. To explain this behavior, the surface activity properties of chitosan at the air–solution interface were studied. The variations of the interfacial tension, γ_int, with chitosan concentration and temperature, were also determined. The results were discussed in terms of the modification of the air–water interface owing to the presence of chitosan in the subphase and the surface activity. It was found that the standard free energy of adsorption, , values were dependent on the degree of acetylation (DA) over the DA range being studied. Copyright © 2004 Society of Chemical Industry     

Synthesis and aqueous solution behavior of hydrophobically modified polyelectrolytes

The hydrophobically modified polyelectrolytes were prepared by a micellar technique from acrylamide, n‐alkylacrylamides, and a third monomer, sodium acrylate or sodium 2‐acrylamide‐2‐methylpropanesulfonate. Synthesis and solution properties of the terpolymers were studied. In the synthesis process, the type and amount of surfactant and anionic monomers influenced their solution behavior greatly. The terpolymers showed strong synergistic viscosification effects between their ions and hydrophobic groups. Their aqueous brine solutions exhibit high viscosity at low polymer concentration and can maintain the viscosity during aging at a high temperature (80°C). © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3552–3557, 2001     

Amphiphilic diblock copolymers containing poly(N‐hexylisocyanate): Monolayer behavior at the air–water interface

The behavior of amphiphilic diblock copolymers containing 80–89% of poly(N‐hexylisocyanate) (PHIC) with different hydrophobic segments spread at the air–water interface has been studied. Surface pressure‐area isotherms (π‐A) at the air–water interface were determined. It was found that these diblock copolymers form stable monolayers and the isotherms present a pseudoplateau region at low surface pressure, irrespective of the nature of the partner block: poly(styrene) (PS) or poly(isoprene). Surface pressure variation at the semidilute region of the monolayer was expressed in terms of the scaling laws as power function of the surface concentration. The critical exponents of the excluded volume ν obtained for copolymers with PHIC and PS blocks are 0.58 for the copolymer with 85% of PHIC and 15% of PS, and 0.63 for the copolymer with 89% of PHIC and 11% of PS. The hydrophobicity degree of the diblock copolymers was estimated from the determination of the surface energy values by wettability measurements. The morphology of the monolayers was determined by means of Brewster angle microscopy. Molecular dynamic simulation was performed to explain the experimental behavior of diblock copolymers at the air–water interface. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Water‐solution properties of a hydrophobically modified poly(N‐isopropylacrylamide)

To study the water‐solution properties of a hydrophobically modified poly(N‐isopropylacrylamide) (PNIPAM) which is temperature‐sensitive, the copolymer of N‐isopropylacrylamide (NIPAM) and octadecyl acrylate (ODA) was synthesized. The aggregation behavior of the copolymer was studied by surface tension and fluorescence probe methods. Simultaneously, the phenomenon of the lower critical solution temperature (LCST) of the copolymer in an aqueous solution with increase of the temperature was also studied using the fluorescence probe method. The results showed that phase separation occurred in an aqueous solution of the copolymer when the temperature was increased to its LCST. The π‐A isotherms for the copolymer molecules, as an insoluble monolayer on the water–air interface, was determined by the Langmuir–Blodgett (L–B) method. The abnormal phenomenon, by which the monolayer of the copolymer molecules became more and more condensed with increase of the temperature, was observed. It further indicated that phase separation of the copolymer occurred by another method. In addition, to prove the thermosensitive effect of the copolymer on the release behavior of liposomes, small unilamellar vesicles entrapped with 5(6)‐carboxyfluorescein [5(6)‐CF] were coated with the copolymer. We found that the coating of the copolymer resulted in the reduction of the release below 30°C and enhancement of the release above 30°C, indicating that there are obvious interactions between the copolymer and the liposomes. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 247–255, 2000     

Poly(9‐vinylcarbazole)/silver composite nanotubes and networks formed at the air–water interface

Silver‐nanoparticle‐doped poly(9‐vinylcarbazole) (PVK) nanocomposites were prepared via the reduction of Ag⁺ ions and the self‐assembly of PVK on AgNO₃ aqueous solution surfaces. The formed composite nanostructures depended strongly on the experimental temperature. Thick round disks of PVK surrounded by discrete Ag nanoparticles and/or with irregular holes formed at room temperature; nanotubes and micronetworks doped with Ag nanoparticles formed at about 30–40°C, and networks formed at higher temperature. Further investigation revealed that the nanotubes were transformed from thin round disks. The length of the PVK/Ag composite nanotubes were longer than 10 μm, and the average size of the embedded Ag nanoparticles was found to be about 3.5 nm. The composite networks were composed of round pores with diameters of several hundred nanometers and fine silver nanoparticles embedded in the thin polymer films that covered the pores. The formation of the nanotubes was a very interesting self‐assembly phenomenon of the polymer at the air–water interface that has not been reported before. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Dynamics of pristine graphite and graphene at an air‐water interface

We examine the dynamics and morphology of graphitic films at an air‐water interface in a Langmuir trough by varying interfacial surface coverage, by observing in situ interfacial structure, and by characterizing interfacial structure of depositions on mica substrates. In situ interfacial structure is visualized with Brewster angle microscopy and depositions of the interface are characterized with atomic force microscopy and field‐emission scanning electron microscopy. Compression/expansion curves exhibit a monotonically decreasing surface pressure between consecutive compressions, but demonstrate a “rebound” of hysteretic behavior when the interface is allowed to relax between consecutive compressions. This dynamic results from a competition between consolidation of the interface via agglomeration of particles or the stacking of graphene sheets, and a thermally‐driven relaxation where nanometer‐thick particles are able to overcome capillary interactions. These results are especially relevant to applications where functional films with controlled conductivity and transparency may be produced via liquid‐phase deposition methods. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3177–3187, 2018     

Solution properties of hydrophobically modified polyelectrolytes synthesized via solution and micellar copolymerization

Hydrophobically modified polyelectrolytes (HMPEs) were synthesized using sodium 2‐acrylamido‐2‐methyl‐propanesulfonate and N‐n‐dodecylacrylamide as monomers with the same feeding ratio via micellar and solution copolymerization. The effects of hydrophobic association and electrostatic interaction on the solution properties of the HMPEs were studied. Compared with HMPE obtained via solution copolymerization (s‐PAD), the hydrophobic interaction of HMPE obtained via micellar copolymerization (m‐PAD) is more obvious due to the micro‐blocky distribution of hydrophobic groups. The viscosity properties of m‐PAD in deionized water or brine follow well the scaling theory of polyelectrolytes. However, for s‐PAD, the concentration where zero‐shear viscosity (η₀) and solvent viscosity (η_s) follow η₀ ≈ 2η_s is more likely to be critical entanglement concentration (c_e) rather than critical overlap concentration (c*). It is suggested that modifying of the transition region from c* to c_e is valid and reasonable for s‐PAD. It is believed that the different solution properties of s‐PAD and m‐PAD should be attributed to the distributions of hydrophobic groups in the chains. Copyright © 2010 Society of Chemical Industry     

壳聚糖醋酸溶液中聚集体形貌研究

采用稳态荧光技术和原子力显微镜研究了DD88％壳聚糖醋酸溶液中的聚集行为。30℃0．3mol／L醋酸溶液中壳聚糖的临界聚集浓度为1.5g／L。低于临界聚集浓度时,壳聚糖聚集体表现为大量高度约0．6～3．5nm、轮廓长度约120-340nm的小尺寸聚集体和少量尺寸分布不均一的高度约为8nm,轮廓长度200～400nm的大尺寸聚集体,高于临界聚集浓度时,大尺寸聚集尺寸增加,分布变宽。     

疏水修饰磁性壳聚糖载药纳米粒子的制备与表征

利用O-羧甲基壳聚糖(O-CMC)的表面多种官能团(如-NH_2,-OH,-COOH等)与胆酸(CA)进行化学修饰得到两亲性共聚物,再以反溶剂法将Fe_3O_4和阿霉素(DOX)包埋在两亲性共聚物疏水的核中,制备两亲性的磁性壳聚糖载药纳米粒子,并对磁性载药纳米粒子的形貌、粒径大小、磁性、药物控释等进行了研究。结果表明:磁性壳聚糖纳米粒子有较高的药物包埋效率(92.3%),与自由阿霉素相比,磁性复合物具有明显的缓释作用和pH响应性;同时,有较好的超顺磁性。这些说明制备的疏水修饰磁性壳聚糖载药纳米粒子具有双重响应性,有望作为药物输送载体对肿瘤进行实时跟踪、诊断和治疗。     

Study of rheological behavior of hydrophobically modified hydroxyethyl cellulose

Hydrophobically modified hydroxyethyl cellulose (BD‐HAHEC) was synthesized by the macromolecular reaction of hydroxyethyl cellulose (HEC) with bromododecane (BD). Study of the effects of polymer concentration, shear rate, temperature, and electrolytes on the rheological behavior of BD‐HAHEC indicated that the polymers had high viscosity, excellent viscosity retention in brine water, good thermal stability, and surface activity. Furthermore, investigation of the micromorphology of BD‐HAHEC solutions revealed the close relationship of rheological behavior and a hydrophobically associating effect. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3346–3352, 2006     

Phase transition phenomena of the adsorbed 1-dodecanol monolayer at the air–water interface

Phase transition phenomenon of the 1-dodecanol monolayer at the air/water interface was studied by the dynamic γ(t) curves and the adsorption isotherm obtained by ellipsometry at 20 °C. The surface-concentration adsorption isotherm clearly showed three abrupt increases at bulk concentration C of 1.3 × 10⁻⁹, 2 × 10⁻⁹ and 3.7 × 10⁻⁹ mol/mL, respectively. The 1st and the 3rd transitions observed herein, that were typical 2D first-order transitions, were consistent with the gas to liquid expanded (G–LE) and the liquid expanded to liquid condensed (LE–LC) phase transitions observed in a previous tensiometry study. The 2nd transition that occurred at C = 2 × 10⁻⁹ mol/mL was not identified from any previous dynamic surface-tension profiles. Judging from the substantial increase in the film thickness of the transition, it was believed that the orientation change of the adsorbed molecule was involved in the LE phase. A LE_h and a LE_v phase, that denoted the “lie-down” and “stand-up” types of adsorption, respectively, was used to describe this transition and a cusp, instead of a constant surface-tension region, was observed in the dynamic γ(t) curves for this transition. This suggested that, since the surface tension varied during the transition process, the newly identified LE_h and LE_v transition might not be the typical first-order type of phase transition.     

Properties of hydrophobically modified polyacrylamide with low molecular weight and interaction with surfactant in aqueous solution

Hydrophobically modified polyacrylamide (HMPAM), with a molecular weight of 10⁴ g/mol, was studied using a range of rheological methods and dynamic light scattering (DLS). DLS measurements indicate that the association of the modified polymer begins at low concentration. The modified polymer with high substitution forms transient networks below the critical concentration, but the networks are disrupted by the micelles formed by the polymer itself, and the networks do not contribute to viscosity enhancement. The modified polymers exhibited surface activity, and so they may be regarded as nonionic polymeric surfactants rather than thickeners. On the other hand, HMPAM is shown to interact with the surfactant SDS while PAM is inert to SDS. In the hydrophobic domains, it undergoes a surfactant‐induced association process; in the hydrophobe‐surfactant transition regions, the surfactant binds to the polymer in a noncooperative way and forms a polymer–surfactant complex. Contracted polymer chains begin to extend because of electrostatic repulsion, which can overcome the association at surfactant domains. The conformation of HMPAM polymer chains could be controlled by adding a specific amount of surfactant. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4348–4360, 2006     

Homogeneous synthesis of linoleic acid‐grafted chitosan oligosaccharide in ionic liquid and its self‐assembly performance in aqueous solution

A water‐soluble amphiphilic derivative of chitosan oligosaccharide (COS) modified with linoleic acid (LA)‐grafted COS (LCOS) has been synthesized in the ionic liquid 1‐butyl‐3‐methylimidazolium acetate ([BMIM]Ac). The effects of the ionic liquid on the degree of substitution (DS), surface activity, and self‐assembly behavior of LCOS have been investigated. The results showed that the ionic liquid homogeneous system led to a relatively higher DS compared with the product synthesized in a traditional organic solvent. Furthermore, the LCOS synthesized in the ionic liquid had better surface activity (cmc = 1.1 × 10^?4 g·mL^?1), and could also self‐assemble into nanomicelles with better‐defined spherical shape and a narrower particle size distribution (30–40 nm) in aqueous solution. These results suggest that an effective and environmentally friendly synthesis method for COS derivatives has been established and, moreover, the obtained LCOS micelles meet the basic requirements for use as an improved drug transduction vector. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41727.     

Viscoelastic sol–gel state of the chitosan and alginate solution mixture

The rheological behavior of chitosan/alginate solutions was investigated in relation to gelation and polyelectrolyte complex (PEC) formation. Before mixing, the chitosan and the alginate solutions were both homogeneous fluids. However, heterogeneity developed after mixing, accompanied by a serious increase of viscosity. To determine the sol–gel state of the solutions, the viscoelastic variables, such as the dynamic storage modulus (G′) and loss modulus (G″), the loss tangent, and the viscoelastic exponents for G′ and G″, were obtained. Depending on the concentration, the chitosan/alginate solutions revealed unexpected rheological behavior. At a polymer concentration of 1.0 wt %, the chitosan/alginate solution was in a viscoelastic gel state, whereas, at higher concentrations, viscoelastic sol properties were dominant. A viscoelastic gel state for the chitosan/alginate solution was induced based on the weak formation of fiber‐shaped precipitates of a PEC at a low polymer concentration. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1408–1414, 2007     

Self‐assembling metal coatings from phosphated and siloxane‐modified polyurethane dispersions: An analysis of the coating–air interface

Polyurethane dispersion coatings containing phosphate and siloxane chains were evaluated for their self‐assembling properties for a single‐coating system. Dynamic contact angles (DCAs) and X‐ray photoelectron spectroscopy (XPS) were used to study the coating–air interface. The siloxane chains were the predominant species on the surfaces of the coatings. The wetting properties of the coating–air interface were reversed when the coated panels were immersed in an ionic solution, and the decrease in hydrophobicity was linear with time. Results from XPS and DCA analyses were similar. The self‐assembling properties of the coatings could be useful in the development of hydrophobic coatings from hydrophilic polymers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 893–899, 2003     

Bioadhesive hydrophobic chitosan microparticles for oral delivery of insulin: In vitro characterization and in vivo uptake studies

Hydrophobically modified polymeric matrices for drug delivery were developed by N‐acylation of chitosan with long(C₁₈) and medium chain(C₈) fatty acid chlorides like octanoyl and oleoyl chloride. Chemical modifications of chitosan were confirmed by IR spectra and trinitrobenzenesulphonic acid assay. Modified chitosan particles were prepared by ionotropic gelation with sodium tripolyphosphate. Hydrophobic modification was confirmed by contact angle measurements. Scanning electron micrographs showed the presence of compact microparticles. Swelling studies showed that oleoyl chitosan exhibited low swelling profile than octanoyl chitosan at acidic pH. In vitro release profile at pH 7.4 showed that about 90% of insulin was released by 5th hour. ELISA studies proved that the microparticles were capable of maintaining biological activity of insulin. Mucoadhesion studies proved that oleoyl derivative was more mucoadhesive than octanoyl derivative. In vivo uptake studies of fluorescent‐labeled microparticles on rat intestinal sections showed that oleoyl chitosan microparticles exhibited significant uptake than octanoyl chitosan. These results suggests that oleoyl moiety would resist degradation by the gastric enzymes and will enhance mucoadhesivity through hydrophobic interactions and also the permeability by loosening the tight junctions, thus making it a useful carrier for oral peptide delivery applications. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Thermal properties of hydrophobically modified methacrylic acid–ethyl acrylate copolymer solutions

The thermal behavior of a water‐soluble associating polymer system, hydrophobically modified alkali‐soluble emulsion (HASE) polymer, was investigated. This polymer contains a methacrylic acid–ethyl acrylate copolymer backbone with 1 mol % of pendant hydrophobic groups grafted to it. The thermal behavior of the HASE polymer exhibits different trends compared to the hydrophobic ethoxylated urethane (HEUR) system. The lifetime of the hydrophobic junction of the HASE polymer increases with temperature due to the increase in the entropy of the system. However, the structural relaxation time decreases with temperature, caused by the enhanced Brownian dynamics of polymer chains. The relaxation behavior of HASE polymers is either governed by the lifetime of the hydrophobic junction, the structural relaxation time, or a combination of both, depending on the degree of network formation and temperature. Temperature studies indicated that the transient network theory proposed by Tanaka and Edwards is inadequate for describing the activation process of hydrophobic junctions in the HASE associative polymer. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 604–612, 2004     

疏水缔合聚合物的合成、表征及其溶液性能研究

采用自由基胶束聚合法,合成了一种疏水缔合型丙烯酰胺-烷基丙烯酸酯共聚物。用1HNMR谱和TEM对该共聚物进行了表征。用旋转黏度计测定了不同疏水基含量的聚合物的溶液性能,考察了温度对聚合物溶液性能的影响,同时研究了外加盐对聚合物溶液形貌的影响。     

改性磁性壳聚糖微球的制备、表征及性能研究

以(NH4)2Fe(SO4)2.6H2O、NH4Fe(SO4)2.12H2O和壳聚糖为原料,经羟丙基化、胺基化,采用一步包埋法制备了一种新型的多胺基化磁性壳聚糖微球。通过正交实验法确定了磁性微球的最佳制备条件,即搅拌速度1200r/min,壳聚糖用量3.0g,环氧氯丙烷用量2.5mL,乙二胺用量2.5mL。并用IR、TG、XRD和SEM对其结构及形貌进行了表征。结果表明,Fe3O4磁性粒子已包埋了一层胺基化壳聚糖。磁性微球胺基含量为2.302mmol/g;呈较规则的球形,平均粒径为209nm,且具有顺磁性和良好的耐酸性。     

Synthesis and viscosity of hydrophobically modified polymers containing dendritic segments

The cycloterpolymerizations of a newly synthesized dendritic quadruple‐tailed hydrophobic diallylammonium chloride with the hydrophilic monomer N,N‐diallyl‐N‐carboethoxymethylammonium chloride and sulfur dioxide afforded a series of water‐soluble cationic polyelectrolytes (CPEs) containing various proportions (0–1 mol %) of the hydrophobe. At a shear rate of 0.36 s^?1 at 30°C, salt‐free water solutions of the CPEs (4 g/dL) containing 0, 0.35, 0.53, 0.65, and 0.93 mol % of the hydrophobe had apparent viscosity values of 140, 1200, 180,000, 308,000, and 858,000 cps, respectively. The study clearly demonstrated an increase in the viscosity values with increasing incorporation of the hydrophobes. The CPEs on acidic hydrolysis of the pendant ester groups gave corresponding pH‐responsive cationic acid salts, which upon treatment with NaOH, were converted to the polybetaines (PBs), anionic polyelectrolytes (APEs), and PB/APEs containing various proportions of PB and APE fractions in the polymer chain. The effects of charge type and charge density on the polymer chain were investigated. Polymer surfactant interactions were investigated with the cationic surfactant cetyltrimethylammonium bromide; a considerable increase in the viscosity values of the CPE was observed in the presence of the surfactant. The superior viscosity behavior for the polymers containing the quadruple‐tailed hydrophobe was attributed to the blocky nature of the comonomer. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008