Temperature-Responsive Hyperbranched Amine-Based Polymers for Solid–Liquid Separation

Temperature-responsive hyperbranched polymers containing primary amines as pendent groups have been synthesized for solid–liquid separation of kaolinite clay suspension. The effects of temperature, polymer charge density, and polymer architecture on particle flocculation have been investigated. Suspensions treated with the temperature-responsive amine-based hyperbranched polymers showed remarkable separation of the fine particles at a low polymer dosage of 10 ppm and at testing temperatures of 40 °C. In comparison to other polymers studied (linear and hyperbranched homopolymers and copolymers), the temperature-responsive amine-based hyperbranched copolymers showed better particle flocculation at 40 °C, as evidenced by the formation of a thinner sediment bed without compromising the amount of clay particles being flocculated. This superior solid–liquid separation performance can be explained by the hydrophobic interaction of PNIPAM segments on particle surfaces or the capture of additional free particles or small floc due to the exposure of buried positive charges (because of the phase separation of the hydrophilic amines and hydrophobic PNIPAM part) at temperatures above the lower critical solution temperature (LCST)

Study of Bacterial Adhesion on Biomimetic Temperature Responsive Glycopolymer Surfaces

<i>Pseudomonas aeruginosa</i> is an opportunistic pathogen responsible for diseases such as bacteremia, chronic lung infection, and acute ulcerative keratitis. <i>P. aeruginosa</i> induced diseases can be fatal as the exotoxins and endotoxins released by the bacterium continue to damage host tissues even after the administration of antibiotics. As bacterial adhesion on cell surfaces is the first step in bacterial based pathogen infections, the control of bacteria–cell interactions is a worthwhile research target. In this work, thermally responsive poly­(<i>N</i>-isopropylacrylamide) [P­(NIPAAm)] based biomimetic surfaces were developed to study the two major bacterial infection mechanisms, which is believed to be mediated by hydrophobic or lectin–carbohydrate interactions, using quartz crystal microbalance with dissipation. Although, a greater number of <i>P. aeruginosa</i> adhered to the NIPAAm homopolymer modified surfaces at temperatures higher than the lower critical solution temperature (LCST), the bacterium–substratum bond stiffness was stronger between <i>P. aeruginosa</i> and a galactose based P­(NIPAAm) surface. The high bacterial adhesion bond stiffness observed on the galactose based thermally responsive surface at 37 °C might suggest that both hydrophobic and lectin–carbohydrate interactions contribute to bacterial adhesion on cell surfaces. Our investigation also suggests that the lectin–carbohydrate interaction play a significant role in bacterial infections

Temperature- and pH-Responsive Benzoboroxole-Based Polymers for Flocculation and Enhanced Dewatering of Fine Particle Suspensions

Random copolymers based on <i>N</i>-isopropylacrylamide (NIPAAm) containing 2-aminoethyl methacrylamide hydrochloride (AEMA) and 5-methacrylamido-1,2-benzoboroxole (MAAmBo) were synthesized and subsequently evaluated for their performance in solid–liquid separation at various pH and temperatures. The strong interactions between benzoboroxole residues and kaolin hydroxyl groups were evaluated for the first time in the flocculation of fine particle suspensions. The lower critical solution temperatures (LCSTs) of PAMN decreases because of the hydrophobic nature of the benzoboroxole moieties, resulting in strong hydrophobic interaction at temperatures higher than the LCSTs. Temperature and pH responsive polymer, P­(AEMA₅₁-<i>st</i>-MAAmBo₇₆-<i>st</i>-NIPAM₃₈₁) (denoted as PAMN) shows the ability to induce fastest settling at a low dosage of 25 ppm and under the condition of pH 9 and 50 °C. The accelerated settling rate is considered to be due to the strong adhesion of benzoboroxole residues to the kaolin hydroxyl groups, the electrical double layer force, and the hydrophobic force. During condensation phase, increasing the pH of sediment to pH 11 could attain the most compact structure. Random copolymers containing benzoboroxole groups act as dispersants (due to pH-responsive character) rather than flocculants at pH 11, providing repulsive force that enables particles to rearrange their position and consolidate well. Through a two-step solid–liquid separation including settling phase and consolidation phase, rapid settling and compact sediment are feasible simultaneously

Simple Coating with pH-Responsive Polymer-Functionalized Silica Nanoparticles of Mixed Sizes for Controlled Surface Properties

Different-sized silica nanoparticles (SiNPs) were functionalized by pH-responsive poly­(2-(diisopropylamino)­ethyl methacrylate) (PDP) via surface-initiated atom transfer radical polymerization (ATRP). The functionalized PDP-SiNPs were used to coat glass surfaces, polymeric nanofibers, and paper via simple coating methods such as dip, cast, and spray coating. A PDP-SiNPs mixture having different sizes was found to change the surface properties of the substrates remarkably, compared to one containing PDP-SiNPs with uniform sizes. High surface roughness was achieved with very little coating materials, which is beneficial from an economical point of view. Moreover, adsorption/desorption of PDP-SiNPs onto/from the substrates could be controlled by changing solution pH due to the protonation/deprotonation of the PDP. The surface properties of the coated substrates were analyzed by contact angle (CA) measurement, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). This inexpensive system provides a simple, quick, and effective approach to changing the surface properties of substrates that could be exploited for large-scale surface modification

Self-Healing and Injectable Shear Thinning Hydrogels Based on Dynamic Oxaborole-Diol Covalent Cross-Linking

Hydrogels containing sugar and oxaborole residues with remarkable self-healing properties were synthesized by free-radical polymerization in a facile and one pot process. The strong covalent interactions between the oxaborole residues and free adjacent hydroxyl groups of the pendent sugar residues of the glycopolymer allowed the <i>in situ</i> formation of hydrogels achievable under either neutral or alkaline conditions. These hydrogels showed excellent self-healing and injectability behaviors in aqueous conditions and were found to be responsive to both pH and the presence of free sugars (such as glucose) in solution. Furthermore, these hydrogels can easily be reconstructed from their lyophilized powder into any desired three-dimensional scaffold. Additionally, the hydrogels can be designed to have very low cytotoxicity and hence can be used as a scaffold for cell encapsulation. With these unique properties, these biocompatible, biodegradable, rebuildable, and self-healable hydrogels offer great potential in many biomedical applications