6 research outputs found
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 polyÂ(<i>N</i>-isopropylacrylamide) [PÂ(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 PÂ(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, PÂ(AEMA<sub>51</sub>-<i>st</i>-MAAmBo<sub>76</sub>-<i>st</i>-NIPAM<sub>381</sub>) (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 polyÂ(2-(diisopropylamino)Âethyl
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