Effect of Plasma-Treated Polymer Substrates on Fabricating Surface Microsystems Through LbL Coating

Xuyan Liu,Shen Tang,최홍기,최호석 한국고분자학회 2010 Macromolecular Research Vol.18 No.5

The surface free energy of three polymeric substrates, PMMA (poly(methyl methacrylate)), PS (polystyrene)and PC (polycarbonate), subjected to a RF O2 plasma treatment and washing with water was studied with the aim of fabricating surface micro-systems using a LbL technique. More uniform hysteresis of the deionized(DI) water contact angle after the plasma treatment followed by washing with water was observed on the PS surface compared to that on the PMMA and PC surfaces. XPS showed that washing with water may alter the plasma generated functionality,which readily forms oxygen containing groups, such as C=O and O-C=O. The surface free energy measured by the acid-base method showed that the Lewis base components on PS were less affected than those on PMMA and PC, due to the weak solvent effect of the former. During the LbL coating of the polyelectrolyte, the solvent effect was less likely to occur on PS, which exhibited better electrostatic bonding of the positive and negative polyelectrolytes (PEL). The fluorescence intensity was similar to the above findings, which may help determine the best substrate for surface micro-patterning using the LbL technique.

Changes in the affordability of 4-year public higher education in China during massification

Shuhua Liu,Enhao Wang,Xuyan Wang 서울대학교 교육연구소 2021 Asia Pacific Education Review Vol.22 No.2

This study investigates how the affordability of 4-year public higher-education tuition in China changed during the massification period. To conduct an in-depth analysis, this paper examines a wide range of data from the National Bureau of Statistics and adopts a series of measurement indicators, including average tuition as a percentage of per-capita GDP, its share in per-capita disposable income and family savings, and its ratio to financial aid. First, this study concludes that during massification, college affordability rapidly declined and then continuously increased. While for a significant majority of Chinese families college tuition is not an unbearable financial burden, it remains expensive for households in the lowest-income quintile. Second, this paper sheds light on the gap in residents’ ability to pay higher-education tuition between urban and rural areas, different regions, and different income groups. It finds a rapid widening in the gap in these dimensions during the early years of massification, which in recent years has gradually narrowed. Indeed, the mode of Chinese higher education has quickly transformed from “high tuition and low aid” to “low tuition and high aid.”

Synthesis of microcapsules with polystyrene/ZnO hybrid shell by Pickering emulsion polymerization

Chen, Wenbao,Liu, Xuyan,Liu, Yangshuo,Kim, Hyung-Il Springer-Verlag 2010 Colloid and Polymer Science Vol.288 No.14

Novel Synthesis of Silica/Polypyrrole Hybrid Nanocomposites via Microemulsion Polymerization with a Vapor Monomer Feeding System

Wenbao Chen,Xuyan Liu,Yangshuo Liu,방영길,김형일 한국고분자학회 2011 Macromolecular Research Vol.19 No.1

Silica/polypyrrole hybrid nanoparticles were synthesized by microemulsion polymerization using a vapor monomer feeding system. In contrast to the traditional monomer feeding methods of microemulsion polymerization,this study examined the monomer feeding as a vapor phase. The silica modified with 3-(trimethoxysilyl)propyl methacrylate had a hydrophobic surface was used as template. Polymerization of the pyrrole monomers occurred at the surface of the modified silica. By controlling the vapor feeding speed, the pyrrole monomer could be dispersed in the reaction system quite well. The modification of silica and the formation of silica/polypyrrole nanoparticles were characterized by Fourier transform infrared spectroscopy and thermogravimetric analysis. The silica/polypyrrole hybrid morphology was confirmed by transmission electron microscopy and scanning electron microscopy. Through a comparison with the nanoparticles made by traditional microemulsion polymerization, uniform and smaller nanoparticles of the silica/polypyrrole hybrid nanocomposite were prepared using a lower surfactant content. The size of the silica/polypyrrole nanocomposites decreased with increasing surfactant content and decreasing pyrrole monomer content.

Fabrication and characterization of microcapsules with polyamide–polyurea as hybrid shell

Chen, Wenbao,Liu, Xuyan,Lee, Dong Weon Springer-Verlag 2012 JOURNAL OF MATERIALS SCIENCE - Vol.47 No.4

Graft copolymerization kinetics of acrylic acid onto the poly(ethylene terephthalate) surface by atmospheric pressure plasma inducement

Wang, Jiku,Liu, Xuyan,Choi, Ho-Suk Wiley Subscription Services, Inc., A Wiley Company 2008 Journal of polymer science Part B, Polymer physics Vol.46 No.15

<P>After one atmospheric pressure plasma treatment of poly(ethylene terephthalate) (PET) film, acrylic acid (AAc) in aqueous solution was successfully graft-copolymerized onto PET films. The effects of reaction time, AAc monomer concentration and reaction temperature on grafting behavior of AAc were systematically studied. Possible reaction kinetics of plasma-induced graft copolymerization, starting from initial hydroperoxide decomposition, were proposed. Through the Arrhenius analysis about graft copolymerization kinetics of AAc monomers on PET surface, it was revealed that the activation energies of decomposition, propagation and termination were 98.4, 63.5, and 17.5 kJ/mol, respectively. The temperature around 80 °C was favorable not only for the formation of oxide radicals through the thermal decomposition of hydroperoxide on PET surface but also for the extension of graft copolymer chain through direct polymer grafting. Poly(acrylic acid) (PAAc) grains grafted onto PET surfaces possessed relatively uniform size and both PAAc grain size and surface roughness increased with increasing the grafting degree of AAc. The increase of grain size with increasing grafting degree results from the possibility of forming long chain graft copolymers and their shielding of reactive sites. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1594–1601, 2008</P>

Preparation of O/W Pickering emulsion with oxygen plasma treated carbon nanotubes as surfactants

Wenbao Chen,김형일,Xuyan Liu,Yangshuo Liu,Youngkil Bang 한국공업화학회 2011 Journal of Industrial and Engineering Chemistry Vol.17 No.3

The stable oil-in-water Pickering emulsions were prepared using oxygen plasma treated carbon nanotubes (CNTs) as stabilizers. Some hydrophilic groups such as hydroxyl and carboxyl groups were introduced on the surface of the CNTs by plasma treatment. The plasma treated CNTs showed the improvement in dispersion stability in water as well as cyclohexane for a long time. The Raman spectra showed that the original properties of CNTs were retained after the plasma treatment differently from other chemical modification methods. The plasma treated CNTs had a favorable interfacial interaction with water to form the stable O/W Pickering emulsions. The formation of stable O/W Pickering emulsion was dependent on the CNT concentration, the plasma treatment period, and the sonication time.

A Hybrid Cloud Testing System Based on Virtual Machines and Networks

( Jing Chen ),( Honghua Yan ),( Chunxiao Wang ),( Xuyan Liu ) 한국인터넷정보학회 2020 KSII Transactions on Internet and Information Syst Vol.14 No.4

Traditional software testing typically uses many physical resources to manually build various test environments, resulting in high resource costs and long test time due to limited resources, especially for small enterprises. Cloud computing can provide sufficient low-cost virtual resources to alleviate these problems through the virtualization of physical resources. However, the provision of various test environments and services for implementing software testing rapidly and conveniently based on cloud computing is challenging. This paper proposes a multilayer cloud testing model based on cloud computing and implements a hybrid cloud testing system based on virtual machines (VMs) and networks. This system realizes the automatic and rapid creation of test environments and the remote use of test tools and test services. We conduct experiments on this system and evaluate its applicability in terms of the VM provision time, VM performance and virtual network performance. The experimental results demonstrate that the performance of the VMs and virtual networks is satisfactory and that this system can improve the test efficiency and reduce test costs through rapid virtual resource provision and convenient test services.

VC-dimension and distance chains in $\mathbb{F}_q^d$

Ruben Ascoli,Livia Betti,Justin Cheigh,Alex Iosevich,Ryan Jeong,Xuyan Liu,Brian McDonald,Wyatt Milgrim,Steven J. Miller,Francisco Romero Acosta,Santiago Velazquez Iannuzzelli 강원경기수학회 2024 한국수학논문집 Vol.32 No.1

Given a domain $X$ and a collection $\mathcal{H}$ of functions $h:X\to \{0,1\}$, the Vapnik-Chervonenkis (VC) dimension of $\mathcal{H}$ measures its complexity in an appropriate sense. In particular, the fundamental theorem of statistical learning says that a hypothesis class with finite VC-dimension is PAC learnable. Recent work by Fitzpatrick, Wyman, the fourth and seventh named authors studied the VC-dimension of a natural family of functions $\mathcal{H}_t^{'2}(E): \F_q^2\to \{0,1\}$, corresponding to indicator functions of circles centered at points in a subset $E\subseteq \mathbb{F}_q^2$. They showed that when $|E|$ is large enough, the VC-dimension of $\mathcal{H}_t^{'2}(E)$ is the same as in the case that $E = \mathbb F_q^2$. We study a related hypothesis class, $\Hh_t^d(E)$, corresponding to intersections of spheres in $\mathbb{F}_q^d$, and ask how large $E\subseteq \mathbb{F}_q^d$ needs to be to ensure the maximum possible VC-dimension. We resolve this problem in all dimensions, proving that whenever $|E|\geq C_dq^{d-1/(d-1)}$ for $d\geq 3$, the VC-dimension of $\Hh_t^d(E)$ is as large as possible. We get a slightly stronger result if $d=3$: this result holds as long as $|E|\geq C_3 q^{7/3}$. Furthermore, when $d=2$ the result holds when $|E|\geq C_2 q^{7/4}$.

Facile Synthesis of Ag/AgCl Grafted AgBi(MoO4)2 with Enhanced Photocatalytic Performance Under Visible Light

Xu Yan,Ziyang Wu,Yong Zhao,Biao Liu,Yong Zhao 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2018 NANO Vol.13 No.08

Silver nanoparticles (NPs) and related semiconductors are a family of very important and widely applied photocatalysts. However, the preparation of high stability and activity of this photocatalyst is still a challenge. In this work, we report a stable Ag/AgCl/AgBi(MoO4)2 heterojunction photocatalyst fabricated via a simple in situ anion-exchange reaction followed by the photoreduction treatment. In the treatment of tetracycline (TC) wastewater under visible light, the AC-0.4 sample (prepared with 0.4 mmol KCl) exhibits the significantly improved activity (degradation ratio, DR of 71.3%) compared with the pristine AgBi(MoO4)2 (30% DR) and Ag/AgCl sample (synthesized by the photoreduction of AgCl) (37% DR) under identical experimental conditions. This activity promotion is from the fast interfacial electron transfer between the heterojunction phases of AgCl/AgBi(MoO4)2 and the SPR effect of Ag NPs. After five successive recycles, the AC-0.4 sample still maintains good stability and activity for TC degradation, which shows a great potential to be used in practical application. Through the ESR and controlled scavenged experiments, we found the · OH and · O- 2 are the major reactive intermediate species in the TC photodegradation reaction. Our work provides a new insight into the synthesis of stable and high efficient Ag-based heterojunction photocatalysts for the application of wastewater treatment.