Wettability of biodegradable surfaces

The study of the interfacial characteristics of biodegradable polymers/copolymers is of importance from the point of view of both surface science and pharmaceutical/cosmetic applications. Films formed from biodegradable polymers allow systematic wettability studies on surfaces with a wide range of copolymer (chemical) compositions. The possibility of interchanging these drug carrier polymers, if their wetting characteristics are similar, could be beneficial to diverse applications. Low-rate dynamic contact angles on films (solvent cast on polar substrates, i.e. on silicon wafer) of poly(lactic acid), and its copolymers with poly(glycolic acid), (with four different copolymer ratios of 85/15, 75/25, 65/35 and 50/50) were measured by axisymmetric drop shape analysis-profile (ADSA-P) with four liquids: water, formamide, 2,2′-thiodiethanol and 3-pyridylcarbinol. The solid surface tensions, γ_sv, were calculated from the advancing contact angles, θ_A. The surface topography of the polymer films was investigated by atomic force microscopy (AFM). The surface composition of the polymer layers was analyzed by X-ray photoelectron spectroscopy (XPS). The advancing contact angles were found to be independent of the composition of the copolymers, while the receding angles, θ_R, did decrease with increasing ratio of the polar component [poly(glycolic acid)] in the copolymers. The solid surface tensions calculated from the advancing contact angles of the liquids for all homo- and copolymers were the same within the error limit; the mean value being γ_sv=35.6 ± 0.2 mJ/m². The surface roughness, which was obtained from AFM images, increased with increasing poly(glycolic acid) ratio, without affecting the advancing contact angles. The constancy of γ_sv is attributed to the effect of the surface activity of the nonpolar segments of the polymer chains, which oriented to form the outermost layer of the film. This was confirmed by XPS analysis. Received: 06 November 2000 Accepted: 09 May 2001     

Surface energy of ethylene-co-1-butene copolymers determined by contact angle methods

Wilhelmy plate measurements of contact angles with a series of test liquids are used to calculate the surface energies of two poly(ethylene-co-1-butene) random copolymers. Results from five methods of calculation are reported: one-liquid (Good-Girifalco and Neumann), two-liquid (harmonic mean and geometric mean), and three-liquid (Lifshitz-van der Waals acid-base) methods. We find that all five methods are sensitive to the choice of test liquids used for contact angle measurements, as previously reported, but consistent results are obtained if recommended combinations of liquids are used. The mean results of the three-liquid acid-base method are judged to be the most reliable and informative, leading to surface energies of 30.8 mJ/m2 for poly(ethylene-co-1-butene) copolymer composed of 92 mol% ethylene and 30.2 mJ/m2 for copolymer composed of 88 mol% ethylene.     

Photoiniferter-based thermoresponsive graft architecture with albumin covalently fixed at growing graft chain end

The aim of this study was to develop a novel surface graft architecture in which albumin is covalently fixed at the growing chain end of the hydrophilic polymers: poly(N, N-dimethylacylamide), PDMAM, and poly(N-isopropylacrylamide), PNIPAM. Photoiniferter-based surface-grafted polymers were prepared using either an albuminated iniferter or a nonalbuminated iniferter, both of which were derivatized on glass surfaces, and ultraviolet (UV)-light-irradiated in the presence of a DMAM or NIPAM monomer. Surface chemical composition analysis by X-ray photoelectron spectroscopy, contact angle measurement, immunostaining using fluorescence labeled antibody and the measurement of graft thickness, as determined from force-distance curves obtained in water at 25 degrees C and 37 degrees C by atomic force microscopy, evidenced that the thickness of graft layer increased with photoirradiation time and albumin molecules exist at growing chain ends. For PNIPAM-grafted surfaces, the interconversion between swollen and collapsed graft chains was observed below and above the lower critical solution temperature of PNIPAM. The potential application of a thermoresponsive graft with albumin covalently fixed at its growing chain end was discussed in terms of "active" nonfouling surface design based on the temperature-dependent switching of phase transition.     

Thin films of PS/PS‐b‐pnipam and ps/pnipam polymer blends with tunable wettability

We developed thin films of blends of polystyrene (PS) with the thermoresponsive polymer poly(N‐isopropylacrylamide) (PNIPAM) (PS/PNIPAM) and its diblock copolymer polystyrene‐b‐poly(N‐isopropylacrylamide) (PS/PS‐b‐PNIPAM) in different blend ratios, and we study their surface morphology and thermoresponsive wetting behavior. The blends of PS/PNIPAM and PS/PS‐b‐PNIPAM are spin‐casted on flat silicon surfaces with various drying conditions. The surface morphology of the films depends on the blend ratio and the drying conditions. The PS/PS‐b‐PNIPAM films do not show an increase in their water contact angles with temperature, as it is expected by the presence of the PNIPAM block. All PS/PNIPAM films show an increase in the water contact angle above the lower critical solution temperature of PNIPAM, which depends on the ratio of PNIPAM in the blend and is insensitive to the drying conditions of the films. The difference between the wetting behavior of PS/PS‐b‐PNIPAM and PS/PNIPAM films is due to the arrangement of the PNIPAM chains in the film. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 670–679     

Linear and comb‐like acrylonitrile/N‐isopropylacrylamide copolymers synthesized by the combination of RAFT polymerization and ATRP

We describe the synthesis of three novel thermoresponsive copolymers of acrylonitrile (AN) with N‐isopropylacrylamide (NIPAM) by a combination of reversible addition‐fragmentation chain transfer (RAFT) polymerization and atom transfer radical polymerization (ATRP). Linear copolymer polyacrylonitrile (PAN)‐b‐PNIPAM was directly prepared by RAFT polymerization. Comb‐like copolymers were synthesized by ATRP using brominated AN/2‐hydroxyethyl methacrylate copolymers as macroinitiators, which were prepared by RAFT polymerization. FT‐IR, NMR, and GPC were employed to characterize the synthesized copolymers. Results indicate that the polymerization processes can be well controlled and the resultant copolymers have well‐defined structures as well as narrow polydispersity. Then dense films were fabricated from these thermoresponsive copolymers and the surface wettability was evaluated by water contact angle measurements at different temperatures. It is found that the surface wettability is temperature‐dependant and both the transition temperature and decrement of water contact angle are affected by the copolymer shapes as well as the length of PNIPAM blocks. Considering the excellent fiber‐ and membrane‐forming properties of PAN‐based copolymers, the obtained thermoresponsive copolymers are latent materials for functional fibers and membranes. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 92–102, 2009     

Properties of superhydrophobic paper treated with rapid expansion of supercritical CO<Subscript>2</Subscript> containing a crystallizing wax

Paper samples were rendered superhydrophobic with Alkyl Ketene Dimer using (1) Airblasting with cryo ground micro particles, (2) crystallizing from organic solvents and (3) spraying with Rapid Expansion of Supercritical Solutions (RESS) technique. The papers were characterized using Scanning Electron Microscopy, contact angle to water measurements and X-ray Photoelectron Spectroscopy (XPS). Advancing contact angles were in the region of 150°–160° and receding contact angles were in the region of 110°–130°. Diagrams showing the drop base diameter vs. the contact angle when water is pumped into, and then withdrawn from, a sessile drop show that a stick slip pattern is present in the advancing phase for a non coated internally sized paper. Papers rendered superhydrophobic with the RESS technique showed a much less pronounced stick slip pattern in the advancing phase but still a stick slip pattern in the receding phase.     

Adsorption and thermoresponsive behavior of poly(N-isopropylacrylamide-co-N,N'-cystaminebisacrylamide) thin films on gold

We describe the synthesis of thermoresponsive polymers made from N-isopropylacrylamide and varying amounts of a thiol-containing co-monomer, N,N'-cystaminebisacrylamide (P(NIPAm-co-CBAm)). Infrared spectroscopy revealed a backbone similar to that seen with pure PNIPAm. UV-vis spectroscopy showed that P(NIPAm-co-CBAm) undergoes a thermoresponsive phase transition around 32 degrees C in aqueous solution. The presence of the thiol groups enabled the polymer to adsorb onto gold surfaces. Following adsorption onto a gold surface, X-ray photoelectron spectroscopy showed a carbon/gold atomic ratio of 0.93 for a sample without CBAm and a ratio of 1.61 for a P(NIPAm-co-CBAm) sample with 0.20% CBAm. Quartz crystal microbalance (QCM) analysis showed increases in the mass of polymer adsorbed when the CBAm content in the polymer increased. The thermoresponsive behavior of the thin films on gold was investigated with contact angle and dissipative QCM analysis. Contact angles were measured for polymer films at both 25 and 60 degrees C. The largest temperature-induced alteration in the contact angle was seen with the 1.00% CBAm sample. Similarly, QCM-D results showed a significantly greater change in frequency and dissipation following a temperature change when CBAm was present than in pure NIPAm polymers.     

Thermoresponsive core-shell microgels with silica nanoparticle cores: size, structure, and volume phase transition of the polymer shell

Core-shell microgels made of the thermoresponsive polymer poly(N-isopropylacrylamide) (PNIPAM) and silica nanoparticles as inorganic cores were investigated by dynamic light scattering (DLS) and small angle neutron scattering (SANS). In order to study the response of the particles upon changes of temperature, experiments were done in a temperature interval close to the volume phase transition temperature of the PNIPAM shell. While DLS probes the hydrodynamic dimensions of the particles, determining their centre of mass diffusion, SANS provides the correlation length xi of the PNIPAM network. Additionally, the composite particles were characterised by electron microscopy as well as atomic force microscopy to reveal the core-shell structure and at the same time the approximate dimensions and the shape of the microgels.     

Click cyclization of linear triblock copolymers at block junctions under high concentration due to end-block shielding

Linear triblock copolymers of poly(N-isopropylacrylamide) (PNIPAM) and poly(ethylene glycol) (PEG) with two azide groups at both block junctions (PNIPAM-N3-PEG-N3-PNIPAM) are click reacted with dipropargyl oxalylate under high polymer concentration (250 g/L). Benefiting from rapid feature of alkyne-azide click reaction and spatial shielding of PNIPAM end blocks, PEG center block of PNIPAM-N3-PEG-N3-PNIPAM remains separated although PNIPAM end blocks keep in contact under this high concentration. Therefore, PNIPAM-N3-PEG-N3-PNIPAM undergoes self-cyclization at block junctions to form tadpole-shaped architecture while N3-PEG-N3 without PNIPAM end blocks inter-connects linearly. The influence of block lengths of PEG and PNIPAM on the unusual cyclization under high polymer concentration is studied.     

Determination of accurate surface tensions of maleimide copolymers containing fluorinated side chain from contact angle measurements

Surface energetics of two fluorinated maleimide copolymers containing fluorinated side chain, i.e., poly(ethene-alt-N-(4-(perfluoroheptylcarbonyl)aminobutyl)maleimide) (ETMF) and poly(octadecene-alt-N-(4-(perfluoroheptylcarbonyl)aminobutyl)maleimide) (ODMF), are studied by contact angle measurements with 10 liquids consisting of fairly bulky molecules. Because of the inertness of octamethylcyclotetrasiloxane (OMCTS) and decamethylcyclopentasiloxane (DMCPS) molecules, their contact angles are used to determine the surface tension of the two polymers. It is found that other liquids show specific interactions with the ETMF films, and their contact angles deviate from a smooth curve that represents the surface tension of ETMF, i.e., 11.00 mJ/m². On ODMF surfaces, only OMCTS and DMCPS yield useful contact angles. Other liquids either dissolve the polymer film or show a slip-stick pattern. This finding is discussed in terms of interactions between segments of the polymer chains and the test liquids. OMCTS and DMCPS are suggested as the appropriate probe liquids, meeting specific criteria necessary for the determination of accurate surface tension of fluoropolymers.     

Thermo-responsive stick-slip behavior of advancing water contact angle on the surfaces of poly(N-isopropylacrylamide)-grafted polypropylene membranes

Wettability of a solid surface is highly important to its practical application,especially for the surface that shows thermoresponsive properties.In this paper,we describe a thermo-responsive stick-slip behavior of water droplets on the surfaces of poly(N-isopropylacrylamide)(PNIPAM)-grafted polypropylene membranes.Field emission scanning electron microscope(FESEM) images elucidate that the morphology of PNIPAM-grafted membrane surface is thermo-responsive,i.e.,the surface becomes rougher above the lower cr...     

Facile strategy for synthesis of silica/polymer hybrid hollow nanoparticles with channels

The silica/polymer hybrid hollow nanoparticles with channels and gatekeepers were successfully fabricated with a facile strategy by using thermoresponsive complex micelles of poly(ethylene glycol)-b-poly(N-isopropylacrylamide) (PEG-b-PNIPAM) and poly(N-isopropylacrylamide)-b-poly(4-vinylpyridine) (PNIPAM-b-P4VP) as the template. In aqueous solution, the complex micelles (PEG-b-PNIPAM/PNIPAM-b-P4VP) formed with the PNIPAM block as the core and the PEG/P4VP blocks as the mixed shell at 45 °C and pH 4.0. After shell cross-linking by 1,2-bis(2-iodoethoxyl)ethane (BIEE), tetraethylorthosilicate (TEOS) selectively well-deposited on the P4VP block and processed the sol-gel reaction. When the temperature was decreased to 4 °C, the PNIPAM block became swollen and further soluble, and the PEG-b-PNIPAM block copolymer escaped from the hybrid nanoparticles as a result of swelled PNIPAM and weak interaction between PEG and silica at pH 4.0. Therefore, the hybrid hollow silica nanoparticles with inner thermoresponsive PNIPAM as gatekeepers and channels in the silica shell were successfully obtained, which could be used for switchable controlled drug release. In the system, the complex micelles, as a template, could avoid the formation of larger aggregates during the preparation of the hybrid hollow silica nanoparticles. The thermoresponsive core (PNIPAM) could conveniently control the hollow space through the stimuli-responsive phase transition instead of calcination or chemical etching. In the meantime, the channel in the hybrid silica shell could be achieved because of the escape of PEG chains from the hybrid nanoparticles.     

Synthesis and self‐assembly of thermoresponsive poly(N‐isopropylacrylamide)‐b‐poly(oligo ethylene glycol methyl ether acrylate) double hydrophilic block copolymers

We report on the synthesis of novel poly(N‐isopropylacrylamide)‐b‐poly(oligo ethylene glycol methyl ether acrylate) (PNIPAM‐b‐POEGA) thermoresponsive block copolymers using reversible addition–fragmentation chain transfer polymerization methodologies. The synthesized block copolymers are characterized by gel permeation chromatography, nuclear magnetic resonance, Fourier transform infrared (FTIR) techniques in terms of molecular weight and composition. Their thermoresponsive self‐assembly in aqueous media is investigated using dynamic and static light scattering. The PNIPAM‐b‐POEGA thermoresponsive block copolymers formed aggregates in water by increasing the temperature above the lower critical solution temperature value of PNIPAM block. Solution pH seems to affect the self‐assembly behavior in some cases due to the presence of ? COOH end groups. Therefore, the copolymers were utilized as “smart” nanocarries for the hydrophobic drug indomethacin, implementing a novel encapsulation protocol taking advantage of the thermoresponsive character of the PNIPAM block. The empty and loaded self‐assembled nanocarriers systems were studied by light scattering techniques, ultraviolet–visible, and FTIR spectroscopy, which gave information on the size and structure of the nanocarriers, the drug loading content and the interactions between the drug and the components of the block copolymers. Drug loaded nanostructures show stability at room temperature, due to active drug/block copolymer interactions. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1467–1477     

Poly(3‐hexyl thiophene)‐b‐poly(N‐isopropyl acrylamide): Synthesis and its composition dependent structural,solubility, thermoresponsive,electrochemical, and electronic properties

Conjugated block copolymers consisting of poly(3‐hexyl thiophene) (P3HT) and a thermoresponsive polymer poly(N‐isopropyl acrylamide) (PNIPAM) with varying composition have been synthesized by facile click reaction between alkyne terminated P3HT and azide terminated PNIPAM. The composition‐dependent solubility, thermoresponsive property in water, phase behavior, electrochemical, optical, and electronic properties of the block copolymers were systematically investigated. The block copolymers with higher volume fraction of PNIPAM form thermoresponsive spherical micelles with P3HT‐rich crystalline cores and PNIPAM coronas. Both X‐ray and atomic force microscopic studies indicated that the blocks copolymers showed well‐defined microphase separated nanostructures and the structure depended on the composition of the blocks. The electrochemical study of the block copolymers clearly demonstrated that the extent of charge transport through the block copolymer thin film was similar to P3HT homopolymer without any significant change in the band gap. The block copolymers showed improved or similar charge carrier mobility compared with the pure P3HT depending on the composition of the block copolymer. These P3HT‐b‐PNIPAM copolymers were interesting for fabrication of optoelectronic devices capable of thermal and moisture sensing as well as for studying the thermoresponsive colloidal structures of semiconductor amphiphilic systems. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1785–1794     

Glass bead grafting with poly(carboxylic acid) polymers and maleic anhydride copolymers

Glass beads were etched with acids and bases to increase the surface porosity and the number of silanol groups that could be used for grafting materials to the surfaces. The pretreated glass beads were functionalized using 3‐aminopropyltriethoxysilane (APS) coupling agent and then further chemically modified by reacting the carboxyl groups of carboxylic acid polymers with the amino groups of the pregrafted APS. Several carboxylic acid polymers and poly(maleic anhydride) copolymers, such as poly(acrylic acid) (PAA), poly(methacrylic acid) (PMA), poly(styrene‐alt‐maleic anhydride) (PSMA), and poly(ethylene‐alt‐maleic anhydride) (PEMA) were grafted onto the bead surface. The chemical modifications were investigated and characterized by FT‐IR spectroscopy, particle size analysis, and tensiometry for contact angle and porosity changes. The amount of APS and the different polymer grafted on the surface was determined from thermal gravimetric analysis and elemental analysis data. Spectroscopic studies and elemental analysis data showed that carboxylic acid polymers and maleic anhydride copolymers were chemically attached to the glass bead surface. The improved surface properties of surface modified glass beads were determined by measuring water and hexane penetration rates and contact angle. Contact angles increased and porosity decreased as the molecular weights of the polymer increased. The contact angles increased with the hydrophobicity of the attached polymer. The surface morphology was examined by scanning electron microscopy (SEM) and showed an increase in roughness for etched glass beads. Copyright © 2007 John Wiley & Sons, Ltd.     

Temperature, pH, and ionic strength induced changes of the swelling behavior of PNIPAM-poly(allylacetic acid) copolymer microgels

The volume phase transition of colloidal microgels made of N-isopropylacrylamide (NIPAM) is well-studied and it is known that the transition temperature can be influenced by copolymerization. A series of poly( N-isopropylacrylamide- co-allylacetic acid) copolymers with different contents of allylacetic acid (AAA) was synthesized by means of a simple radical polymerization approach. The thermoresponsive behavior of these particles was studied using dynamic light scattering (DLS). Further characterization was done by employing transmission electron microscopy (TEM) and zeta potential measurements. TEM observations reveal the approximately spherical shape and low polydispersity of the copolymer particles. In addition, the measured zeta potentials provide information about the relative surface charge. Since these copolymers are much more sensitive to external stimuli such as pH and ionic strength than their pure PNIPAM counterparts, the volume phase transition was investigated at two different pH values and various salt concentrations. At pH 10 for the copolymer microgels with the highest AAA content, a significant shift of the volume phase transition temperature toward higher values is found. For higher AAA content, a change in pH from 8 to 10 can induce a change in radius of up to 100 nm making the particles interesting as pH controlled actuators.     

PNIPAM chain collapse depends on the molecular weight and grafting density

This study demonstrates that the thermally induced collapse of end-grafted poly(N-isopropylacrylamide) (PNIPAM) above the lower critical solution temperature (LCST) of 32 degrees C depends on the chain grafting density and molecular weight. The polymer was grafted from the surface of a self-assembled monolayer containing the initiator (BrC(CH3)2COO(CH2)11S)2, using surface-initiated atom transfer radical polymerization. Varying the reaction time and monomer concentration controlled the molecular weight, and diluting the initiator in the monolayer altered the grafting density. Surface force measurements of the polymer films showed that the chain collapse above the LCST decreases with decreasing grafting density and molecular weight. At T > LCST, the advancing water contact angle increases sharply on PNIPAM films of high molecular weight and grafting density, but the change is less pronounced with films of low-molecular-weight chains at lower densities. Below the LCST, the force-distance profiles exhibit nonideal polymer behavior and suggest that the brush architecture comprises dilute outer chains and much denser chains adjacent to the surface.     

Design, synthesis, and aqueous aggregation behavior of nonionic single and multiple thermoresponsive polymers

Nonionic water-soluble poly(acrylamide)s and poly(acrylate)s were synthesized by RAFT and ATRP methods. Similar to the synthesized poly(N-isopropylacrylamide) and poly(N-acryloylpyrrolidine), aqueous solutions of statistical acrylate copolymers bearing two different oligo(ethylene oxide) side chains showed a sharp clouding transition upon heating beyond characteristic temperatures. The temperature of the cloud point can be easily fine tuned by the copolymer composition. As for poly(N-isopropylacrylamide) and poly(N-acryloylpyrrolidine), the cloud-point temperatures of these statistical copolymers are rather insensitive to changes in the molar mass or the NaCl content of the solutions. Also, ternary triblock copolymers containing one permanently hydrophilic block and two different thermoresponsive blocks were synthesized, varying the block sequence systematically. Their aggregation in aqueous solution was followed by turbidimetry and dynamic light scattering. Depending on the heating process and the triblock sequence, micellar aggregates of 40 to 600 nm size were found. The thermally induced aggregation behavior depends sensitively on the block sequence but is also subject to major kinetic effects. For certain block sequences, a thermally induced two-step association is observed when heating beyond the first and second cloud points of the thermoresponsive blocks. However, the thermal-transition temperatures of the block polymers can differ from the thermal-transition temperatures of the individual homopolymers. This may be caused by end-group effects but also by mutual interactions of the different blocks in solution, as physical mixtures of the homopolymers exhibit deviations from a purely additive thermal behavior.     

AuNPs/PNIPAM复合颗粒的制备及其温敏性质

将金纳米颗粒(AuNPs)组装到聚N-异丙基丙烯酰胺(PNIPAM)水凝胶微球表面制备出AuNPs/PNIPAM复合颗粒. 将PNIPAM 凝胶的温敏特性与AuNPs的光学性质结合, 通过改变温度调节AuNPs的局部表面等离子共振(LSPR)吸收峰位置. 研究结果表明, 温度升高使AuNPs的LSPR吸收峰发生红移, 并且这种效应是可逆的. 同时发现, AuNPs的光学性质还可以作为表征PNIPAM水凝胶微球温敏行为的一种手段. 利用透射电镜、紫外-可见光谱仪及动态光散射仪对AuNPs/PNIPAM复合颗粒的形貌、光学性质、粒径变化等进行了分析.     

Stick-slip of the three-phase line in measurements of dynamic contact angles

Contact angles of a series of n-alkanes (i.e., n-heptane to n-hexadecane) are studied on two functionalized maleimide copolymers (i.e., poly(ethene-alt-N-(4-(perfluoroheptylcarbonyl)aminobutyl)maleimide) (ETMF) and poly(octadecene-alt-N-(4-(perfluoroheptylcarbonyl)aminobutyl)maleimide) (ODMF)). On the homogeneous ETMF films, all liquids show a smooth motion of the three-phase line. In contrast, on ODMF surfaces that are found to consist of mainly fluorocarbons and small patches of hydrocarbons, short-chain n-alkanes show a stick-slip pattern. By increasing the chain length of the probe liquids, stick-slip is reduced significantly. The phenomenon is discussed in the framework of the Cassie equation. It is found that the upper limit of contact angles in the stick-slip pattern is given by the advancing angle that would be obtained on the pure fluorocarbon surface, whereas the lower limit of the stick-slip pattern is given by the Cassie angle.