Contrasting acrylate versus methacrylate crosslinking reactions and the impact of temperature

Divinyl monomers containing multiple vinyl groups are commonly used in polymerization reactions to introduce crosslinked networks. The reactivity of the second vinyl group in a crosslinker monomer decreases once it becomes incorporated in a polymer chain. This Reduced Reactivity Parameter (Ψ) depends on the monomer-crosslinker pair. To date, our group has developed this concept exclusively from methacrylate-based copolymerization systems1,2. Acrylate co-monomers introduce another level of complexity from a competing mechanism toward gel content and macromolecular network development; long chain branching from chain transfer to polymer. The later form networks via α-hydrogen abstraction, which is a prominent reaction with acrylates. Moreover, the differences in reactivity ratio between acrylates and methacrylates add another layer of heterogeneity through the polymerization which also impacts the kinetics and ultimate network structure. In this work, we compare the network formation reaction and the Ψ-parameters for 1,4 butanediol dimethacrylate (BDDMA, containing methacrylate groups) with its acrylate-based counterpart (BDDA, containing acrylate groups) in copolymerization reactions with either n-butyl methacrylate (nBMA) or n-butyl acrylate (nBA). The Ψ-parameter for all systems is estimated by comparing the experimental results with Monte Carlo simulations of the polymerization reactions. The goal of the work is to decouple the contributions of pendent-vinyl based crosslinking and long-chain branching (α-hydrogen abstraction) from the resulting kinetic profile that the Ψ parameter is determined from. Moreover, we contrast the balance of contributions from propagation, chain transfer, reactivity ratios, and utility of the pendent vinyl groups for crosslinking between reactions at either 60 or 70 °C. Even this seemingly small shift in temperature has a marked impact on the kinetics and resulting network for the different pairs of (meth)acrylate comonomers. Tripathi, A.K.; Neenan, M.L.; Sundberg, D.C.; Tsavalas, J.G., Influence of n-Alkyl Ester Groups on Efficiency of Crosslinking for Methacrylate Monomers Copolymerized with EGDMA: Experiments and Monte Carlo Simulations of Reaction Kinetics and Sol-Gel Structure , Polymer (2016), 96, 130–145, DOI:10.1016/j.polymer.2016.04.017 Tripathi, A.K.; Tsavalas, J.G.; Sundberg, D.C., “Monte Carlo Simulations of Free Radical Polymerizations with Divinyl Crosslinker: Pre- and Post-Gel Simulations of Reaction Kinetics and Molecular Structure , Macromolecules (2015) 48, 184−197, DOI: 10.1021/ma502085

THE BALANCE EFFECT OF REARFOOT WEDGES WITH DIFFERENT HEIGHT FOR COLLEGIATE STUDENTS WITH CHRONIC ANKLE INSTABILITY: PILOT STUDY

Chronic ankle instability (CAI) is caused by recurrent lateral ankle sprain. Foot orthotic is one option of treatment. The purpose of this study was to determinate the balance effect of rearfoot wedges with different height in collegiate students with chronic ankle instability. Eight collegiate students with CAI subjects were voluntarily particapated in this study. The area of center of pressure was used as balance variable of outcome measurement. Seven height of rearfoot wedge was used to test, included 0°, 2°, 4°, 6° of medial wedge and 2°, 4°, 6° of lateral wedge. One-way ANOVA was used to analyze the difference among sevent height of wedge intervention in CAI group. The results were showed no significantly difference among seven height of wedge intervention. However, we found a trend of balance improvement with the wedge intervention, especially in 4 degrees of medial wedge intervention

Mechanistic insights into topological network formation in free radical co-polymerization

The first part of the talk will discuss reaction kinetics and molecular architecture development during free-radical, bulk copolymerizations of a homologous series of methacrylate monomers with a series of dimethacrylate crosslinkers of varying alkyl spacer lengths. The overall objective of this work was to determine the extent to which the ester side chains of the methacrylate monomers hinder chain-end radical propagation reactions through the pendent vinyl groups of the crosslinking monomer. We have determined that this steric hindrance is quite significant and increases to the point where the sweeping radius of the pendent vinyl can be obstructed by the neighboring monomer ester side groups. The effective sweeping radius of the pendent vinyl can be equivalently expressed by various combinations of dimethacrylate and methacrylate. Please download the file below for full content

Simplified ZrTiOx-based RRAM cell structure with rectifying characteristics by integrating Ni/n + -Si diode

A simplified one-diode one-resistor (1D1R) resistive switching memory cell that uses only four layers of TaN/ZrTiO( x )/Ni/n(+)-Si was proposed to suppress sneak current where TaN/ZrTiO( x )/Ni can be regarded as a resistive-switching random access memory (RRAM) device while Ni/n(+)-Si acts as an Schottky diode. This is the first RRAM cell structure that employs metal/semiconductor Schottky diode for current rectifying. The 1D1R cell exhibits bipolar switching behavior with SET/RESET voltage close to 1 V without requiring a forming process. More importantly, the cell shows tight resistance distribution for different states, significantly rectifying characteristics with forward/reverse current ratio higher than 10(3) and a resistance ratio larger than 10(3) between two states. Furthermore, the cell also displays desirable reliability performance in terms of long data retention time of up to 10(4) s and robust endurance of 10(5) cycles. Based on the promising characteristics, the four-layer 1D1R structure holds the great potential for next-generation nonvolatile memory technology

SENTIMENT ANALYSIS OF CHINESE MICROBLOG MESSAGE USING NEURAL NETWORK-BASED VECTOR REPRESENTATION FOR MEASURING REGIONAL PREJUDICE

Regional prejudice is prevalent in Chinese cities in which native residents and migrants lack a basic level of trust in the other group. Like Twitter, Sina Weibo is a social media platform where people actively engage in discussions on various social issues. Thus, it provides a good data source for measuring individuals’ regional prejudice on a large scale. We find that a resentful tone dominates in Weibo messages related to migrants. In this paper, we propose a novel approach, named DKV, for recognizing polarity and direction of sentiment for Weibo messages using distributed real-valued vector representation of keywords learned from neural networks. Such a representation can project rich context information (or embedding) into the vector space, and subsequently be used to infer similarity measures among words, sentences, and even documents. We provide a comprehensive performance evaluation to demonstrate that by exploiting the keyword embeddings, DKV paired with support vector machines can effectively recognize a Weibo message into the predefined sentiment and its direction. Results demonstrate that our method can achieve the best performances compared to other approaches

Artificial Intelligence and Visual Analytics: A Deep-Learning Approach to Analyze Hotel Reviews & Responses

With a growing number of online reviews, consumers often rely on these reviews to make purchase decisions. However, little is known about managerial responses to online hotel reviews. This paper reports on a framework to integrate visual analytics and machine learning techniques to investigate whether hotel managers respond to positive and negative reviews differently and how to use a deep-learning approach to prioritize responses. In this study, forty 4- and 5-star hotels in London with 91,051 reviews and 70,397 responses were collected and analyzed. Visual analyses and machine learning were conducted. The results indicate most hotels (72.5%) showing no preference to respond to positive and negative reviews. Our proposed deep-learning approach outperformed existing algorithms to prioritize responses