Amphiphilic monomers bridge hydrophobic polymers and water

Water dissolves a hydrophilic polymer, but not a hydrophobic polymer. Many monomers of hydrophilic polymers, however, are amphiphilic, with a hydrophobic vinyl group for radical polymerization, as well as a hydrophilic group. Consequently, such an amphiphilic monomer may form solutions with both water and hydrophobic polymers. Ternary mixtures of amphiphilic monomer, hydrophobic polymer, and water have recently been used as precursors for interpenetrating polymer networks of hydrophilic polymers and hydrophobic polymers of unusual properties. However, the phase behavior of the ternary mixtures of amphiphilic monomer, hydrophobic polymer, and water themselves has not been studied. Here we mix the amphiphilic monomer acrylic acid, the hydrophobic polymer poly(methyl methacrylate), and water. In the mixture, the hydrophobic polymer can form various morphologies, including solution, micelle, gel, and polymer glass. We interpret these findings by invoking that the hydrophobic and hydrophilic groups of the amphiphilic monomer enable it to function as a bridge. That is, the hydrophobic functional group binds with the hydrophobic polymer, and the hydrophilic functional group binds with water. This picture leads to a simple modification to the Flory-Huggins theory, which agrees well with our experimental data. Amphiphilic monomers offer a rich area for further study for scientific insight, as well as for expanding opportunities to develop materials of self-assembled structures with unusual properties.

Reduced Biofilm Formation at the Air-Liquid-Solid Interface via Introduction of Surfactants

Reduced biofilm formation is highly desirable in applications ranging from transportation to separations and healthcare. Biofilms often form at the three-phase interface where air, liquid, and solid coexist due to the close proximity to nutrients and oxygen. Reducing biofilm formation at the triple interface presents challenges because of the conflicting requirements for hydrophobicity at the air-solid interface (for self-cleaning properties) and for hydrophilicity at the liquid-solid interface (for reduced foulant adhesion). Meeting those needs simultaneously likely entails a dynamic surface, capable of shifting the surface energy landscape in response to wetting conditions and thus enabling hydrophobicity in air and hydrophilicity in water. Here, we designed a facile approach to render existing surfaces resistant to biofilm formation at the triple interface. By adding trace amounts (∼0.1 mM) of surfactants, biofilm formation of Pseudomonas aeruginosa (known to form biofilm at the triple interface) was reduced on all surfaces tested, ranging from hydrophilic to hydrophobic, polar to nonpolar. That reduced fouling was not a result of the known antimicrobial effects. Instead, it was attributed to the surface-adsorbed surfactants that dynamically control surface energy at the triple interface. To further understand the effect of surfactant-surface interactions on biofilm reduction, we systematically varied the surfactant charge type and surface properties (surface energy and charge). Electrostatic interactions between surfactants and surfaces were identified as an influential factor when predicting the relative fouling reduction upon introduction of surfactants. Nevertheless, biofilm formation was reduced even on the charge-neutral, fluorinated surface made of poly(1H, 1H, 2H, 2H-perfluorodecyl acrylate) by more than 2-fold simply via adding 0.2 mM dodecyl trimethylammonium chloride or 0.3 mM sodium dodecyl sulfate. Given its robustness, this strategy is broadly applicable for reducing fouling on existing surfaces, which in turn improves the cost-effectiveness of membrane separations and mitigates contaminations and nosocomial infections in healthcare.

The preparation of a novel iron/manganese binary oxide for the efficient removal of hexavalent chromium [Cr(vi)] from aqueous solutions

To remove hexavalent chromium Cr(vi) efficiently, a novel Fe–Mn binary oxide adsorbent was prepared via a “two-step method” combined with a co-precipitation method and hydrothermal method. The as-prepared Fe–Mn binary oxide absorbent was characterized via transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier-transform infrared spectra (FTIR), thermogravimetric analysis (TGA), zeta potential, BET and X-ray photoelectron spectroscopy (XPS). The results indicated that the morphology of the adsorbent was rod-like with length of about 100 nm and width of about 50–60 nm, specific surface area was 63.297 m² g⁻¹, has the composition of α-Fe₂O₃, β-MnO₂ and MnFe₂O₄ and isoelectric point was observed at pH value of 4.81. The removal of Cr(vi) was chosen as a model reaction to evaluate the adsorption capacity of the Fe–Mn binary oxide adsorbent, indicating that the Fe–Mn binary oxide adsorbent showed high adsorption performance (removal rate = 99%) and excellent adsorption stability (removal rate > 90% after six rounds of adsorption). The adsorption behavior of the Fe–Mn binary oxide was better represented by the Freundlich model (adsorption isotherm) and the pseudo-second-order model (adsorption kinetic), suggesting that the adsorption process was multi-molecular layer chemical adsorption. The possible adsorption mechanism of the Fe–Mn binary oxide for the removal of Cr(vi) included the protonation process and the electrostatic attraction interactions.

A novel Fe–Mn binary oxide adsorbent prepared via “co-precipitation and hydrothermal” method, for the efficient and fast removal of Cr(vi).

Efficacy of several additives to modulate the phase behavior of biomedical polymers: A comprehensive and comparative outlook

Several new classes of polymeric materials are being introduced with unique properties. Thermoresponsive polymers (TRPs) are one of the most fascinating and emerging class of biomaterials in biomedical research. The design of TRPs with good response to temperature and its ability to exhibit coil to globular transition behavior near to physiological temperature made them more promising materials in the field of biomaterials and biomedicines. Instead of numerous studies on TRPs, the mechanistic interplay among several additives and TRPs is still not understood clearly and completely. The lack of complete understanding of biomolecular interactions of various additives with TRPs is limiting their applications in interdisciplinary science as well as pharmaceutical industry. There is a great need to provide a collective and comprehensive information of various additives and their behavior on widely accepted biopolymers, TRPs such as poly(N-isopropylacrylamide) (PNIPAM), poly(vinyl methyl ether) (PVME), poly(N-vinylcaprolactum) (PVCL) and poly(ethylene glycol)-poly(propylene glycol)-poly(ethylene glycol) (PEG-PPG-PEG) in aqueous solution. Obviously, as the literature on the influence of various additives on TRPs is very vast, therefore we focus our review only on these four selected TRPs. Additives such as polyols, methylamines, surfactants and denaturants basically made the significant changes in water structure associated to polymer via their entropy variation which is the direct influence of their directly or indirectly binding abilities. Eventually, this review addresses a brief overview of the most recent literature of applications based phase behavior of four selected TRPs in response to external stimuli. The work enhances the knowledge for use of TRPs in the advanced development of drug delivery system and in many more pharmaceutical applications. These kinds of studies provide powerful impact in exploring the utility range of polymeric materials in various field of science.

An efficient study to reach physiological temperature with poly(N-isopropylacrylamide) in presence of two differently behaving additives

HYPOTHESIS

The new findings in the field of polymeric materials expanding their applications in improving the quality of health care are of primary concern. Undoubtedly, the alteration in surface properties of polymeric materials on addition of different additives may provide a step forward towards their better implications in many areas of science. In this regard, the interactions of poly(N-isopropylacrylamide) (PNIPAM) with two differently behaving additives may lead to a new method to carry the phase transition temperature of PNIPAM more near to body temperature so that it can be easily used in drug delivery through intravenous or oral insertion.

EXPERIMENTS

Individually, the addition of sodium dodceylsulfate (SDS) and trimethylamine N-oxide (TMAO) is increasing and decreasing the lower critical solution temperature (LCST) of PNIPAM as compared to classical LCST of PNIPAM in aqueous solution, respectively. In the present study, we try to emphasis the role of mixed SDS and TMAO environment in varying ratios on the phase transition behaviour of PNIPAM. Many biophysical techniques are employed such as UV-visible spectroscopy, fluorescence spectroscopy and dynamic light scattering (DLS), Laser Raman spectroscopy technique and Field emission scanning electron Microscopy (FESEM) for this part of work.

FINDINGS

The SDS is observed to form globules with PNIPAM segments and do not lead to turbidity of solution for the concentration greater than 10 µM. The negatively charged SDS bound PNIPAM globules that do not allow PNIPAM to associate, however; TMAO leads to turbid solution resulted from the hydrophobic association of PNIPAM. SDS is found to be very effective in increasing the LCST up to 62.8 ^°C even at very low (7.5 mM) concentration as compared to decreasing efficiency of TMAO where LCST reaches up to 29.4 ^°C for 0.75 M however, their mixture in specified concentration (1 mM SDS and 0.1 M TMAO) can bring the LCST of PNIPAM very near to body temperature (i.e. ∼36 ^°C) that is quiet promising for its use in target delivery engineering. TMAO ability to counteract the adverse effect of SDS is the main core reason in getting LCST near to body temperature.