Influence of emulsifiers on particle size and particle size distribution of PVC latex synthesized by miniemulsion polymerization

Viet Hung Pham,Young Hwa Lee,Dong Ju Lee,정진석 한국화학공학회 2009 Korean Journal of Chemical Engineering Vol.26 No.6

We synthesized poly(vinyl chloride) (PVC) latexes via miniemulsion polymerization using a mixture of cetyl alcohol (CA) and sodium lauryl sulfate (SLS). A vinyl chloride miniemulsion is easily prepared by conventional mechanical stirring. Experimental design methods were applied to investigate the effects of composition and polymerization conditions on average particle size (APS) and particle size distribution (PSD) of the latexes produced. The APS of the latexes produced ranged from 0.4-0.7 μm. When the APS of the latex produced was above 0.7 μm, the resulting latex was highly unstable. The emulsifier ratio (CA/SLS) was the most prominent factor influencing APS and PSD.

Citrus diaspidids in Viet Nam: New, and confirmation of previous, records based on morphological and molecular verification of taxa

Hang T. Dao,George A.C. Beattie,Gillian W. Watson,Van Lam Pham,Van Liem Nguyen,Duc Khanh Le,Thi Hoa Nguyen,Viet Nguyen,Paul Holford 한국응용곤충학회 2018 Journal of Asia-Pacific Entomology Vol.21 No.1

Armoured scales (Hemiptera: Diaspididae) belong to the largest scale insect family and are among the mostinvasive insects in the world. Accurate identification of armoured scales is essential for systematic and phylogeneticstudies; biogeography; trade and plant quarantine; and pest management, particularly biological control. Several species are serious pests of citrus. Records of past field surveys conducted in Viet Nam between 1967 and2010 indicated the presence of 28 species on citrus there. Discrepancies in these records, and the retention ofspecimens of only five species in collections, led us to undertake surveys throughout the citrus-growing regionsof the country in 2013 and 2014 to verify previous records and conserve voucher specimens. The presence of 21diaspidid species was confirmed based on morphological and molecular data. The species observed werecommon but rarely abundant. Populations in commercial orchards may have been influenced by use of pesticides,but most species were recorded also in gardens and orchards where pesticide use was uncommon. Naturalenemies were abundant, but were not thoroughly documented for all the diaspidids we observed. An identificationkey to the species collected is provided. Differences between our findings and previous records from VietNam, from Yunnan and Guangxi in China, and from Indochinese countries neighbouring Viet Nam, indicate theneed for extensive surveys to fully document the diaspidid fauna on citrus in the region.

Synthesis of epoxy encapsulated organoclay nanocomposite latex via phase inversion emulsification and its gas barrier property

Viet Hung Pham,정진석,하용우,김상훈,정하택,정만용,고봉성,황영준 한국공업화학회 2014 Journal of Industrial and Engineering Chemistry Vol.20 No.1

Waterborne epoxy–clay nanocomposites were prepared by encapsulation of organoclays in epoxy latexparticles via phase inversion emulsification. The organoclays were exfoliated in the epoxy backbonebefore compounding with a hardener and subsequently dispersing in water. The encapsulation of clayplatelets into the waterborne epoxy latex particle resulted in an exponential increase in particle size,from 5 to 10 times at a clay loading of only 1–2 wt%, respectively. The XRD patterns and TEM imagesshow that clay platelets were well intercalated and exfoliated in the epoxy matrix. The gas barrierperformance of the epoxy–clay nanocomposite strongly depended on the kind of organoclay. The bestoxygen barrier efficiency was approximately 14% at 2 wt% clay loading.

Highly Conductive Poly(methyl methacrylate) (PMMA)-Reduced Graphene Oxide Composite Prepared by Self-Assembly of PMMA Latex and Graphene Oxide through Electrostatic Interaction

Pham, Viet Hung,Dang, Thanh Truong,Hur, Seung Hyun,Kim, Eui Jung,Chung, Jin Suk American Chemical Society 2012 ACS APPLIED MATERIALS & INTERFACES Vol.4 No.5

<P>We report a simple, environmentally friendly approach for preparing highly conductive poly(methyl methacrylate)–reduced graphene oxide (PMMA-RGO) composites by self-assembly of positively charged PMMA latex particles and negatively charged graphene oxide sheets through electrostatic interactions, followed by hydrazine reduction. The PMMA latex was prepared by surfactant-free emulsion polymerization using a cationic free radical initiator, which created the positive charges on the surface of the PMMA particle. By mixing PMMA latex with a graphene oxide dispersion, positively charged PMMA particles easily assembled with negatively charged graphene oxide sheets through electrostatic interaction. The obtained PMMA-RGO exhibited excellent electrical properties with a percolation threshold as low as 0.16 vol % and an electrical conductivity of 64 S/m at only 2.7 vol %. Moreover, the thermomechanical properties of PMMA-RGO were also significantly improved. The storage modulus of PMMA-RGO increased by about 30% at 4.0 wt % RGO at room temperature while the glass transition temperature of PMMA-RGO increased 15 °C at only 0.5 wt % RGO.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2012/aamick.2012.4.issue-5/am300297j/production/images/medium/am-2012-00297j_0004.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am300297j'>ACS Electronic Supporting Info</A></P>

Hydrogenated TiO₂@reduced graphene oxide sandwich-like nanosheets for high voltage supercapacitor applications

Pham, Viet Hung,Nguyen-Phan, Thuy-Duong,Tong, Xiao,Rajagopalan, Balasubramaniyan,Chung, Jin Suk,Dickerson, James H. Elsevier 2018 Carbon Vol.126 No.-

<P><B>Abstract</B></P> <P>Hydrogenated TiO<SUB>2</SUB> has recently attracted considerable attention as potential electrode materials for supercapacitors due to its abundance, low cost, high conductivity, remarkable rate capability, and outstanding long-term cycling stability. Herein, we demonstrate the synthesis of hydrogenated TiO<SUB>2</SUB> nanoparticles anchored on reduced graphene oxide nanosheets (HTG) in the form of sandwich-like nanosheet composites. Further, we explored their implementation as electrode materials for high voltage, symmetric supercapacitors, operating in the voltage window of 0–1.8 V. The HTGs were prepared by a sol-gel method, followed by hydrogenation in the temperature range 300–500 °C. Of the prepared composites, HTG prepared at 400 °C exhibited the largest specific capacitance of 51 F g<SUP>−1</SUP> at the current density of 1.0 A g<SUP>−1</SUP> and excellent rate capability with 82.5% capacitance retention as the current density increased 40-fold, from 0.5 to 20.0 A g<SUP>−1</SUP>. HTG's excellent rate capability was attributed to its sandwich-like nanostructure, in which ultrasmall hydrogenated TiO<SUB>2</SUB> nanoparticles densely anchored onto both surfaces of the two-dimensional reduced graphene oxide sheets. Moreover, HTG-based supercapacitors also exhibited long-term cycling stability with the retention over 80% of its initial capacitance after 10,000 cycles. These properties suggest that HTG is a promising electrode material for the scalable manufacture of high-performance supercapacitors.</P> <P><B>Graphical abstract</B></P> <P>Hydrogenated TiO<SUB>2</SUB> has recently attracted considerable attention as potential electrode materials for supercapacitors due to its abundance, low cost, high conductivity, remarkable rate capability, and outstanding long-term cycling stability. In this study, we demonstrate the synthesis of hydrogenated TiO<SUB>2</SUB> nanoparticles anchored on reduced graphene oxide nanosheets (HTG) in the form of sandwich-like nanosheet composites. Further, we explored their implementation as electrode materials for high voltage, symmetric supercapacitors, operating in the voltage window of 0–1.8 V. The HTGs were prepared by a sol-gel method, followed by hydrogenation in the temperature range 300–500 °C. Of the prepared composites, HTG prepared at 400 °C exhibited the largest specific capacitance of 51 F g<SUP>−1</SUP> at the current density of 1.0 A g<SUP>−1</SUP> and excellent rate capability with 82.5% capacitance retention as the current density increased 40-fold, from 0.5 to 20.0 A g<SUP>−1</SUP>. HTG's excellent rate capability was attributed to its sandwich-like nanostructure, in which ultrasmall hydrogenated TiO<SUB>2</SUB> nanoparticles densely anchored onto both surfaces of the two-dimensional reduced graphene oxide sheets. Moreover, HTG-based supercapacitors also exhibited long-term cycling stability with the retention over 80% of its initial capacitance after 10,000 cycles. These properties suggest that HTG is a promising electrode material for the scalable manufacture of high-performance supercapacitors.</P> <P>[DISPLAY OMISSION]</P>

Contamination by persistent organic pollutants and endocrine disrupting chemicals in Vietnam - Patterns, Behavior, Trends and Toxic Potential -

Pham Hung Viet,Tu Binh Minh 환경독성보건학회 2004 한국독성학회 심포지움 및 학술발표회 Vol.- No.-

Current Development of Vector Tracking Loops for Stand-Alone GNSS Receivers in Urban Canyons

Hung Pham-Viet,Sungoh Kwon,Seok Ho Won 한국통신학회 2019 한국통신학회 학술대회논문집 Vol.2019 No.1

Recently, with the development of signal processing methods the accuracy of global navigation satellite system (GNSS) services has been improved. However, in urban environment, since the main challenges are multipath, non-line-ofsight (NLOS), weak signals and low accessibility to satellite in the sky, the positioning is unreliable, inaccuracy, therefore, it decreases the potential for various positioning applications. Vector-based tracking has been applied in modern GNSS receivers as the perfect approach instead of conventional tracking. This paper reviews the literature regarding the performance of vector-based methods applied in GNSS receivers under harsh environments. Under a range of conditions, the vector tracking loops demonstrate their robustness against many error sources in GNSS applications. Moreover, the development as well as the application of different methods based on vector tracking loop also rises a promising for further researches. The goad of paper is to provide the state of art relating to vector tracking loop for future approaches in positioning in urban canyons.

Highly efficient reduction of graphene oxide using ammonia borane

Pham, Viet Hung,Hur, Seung Hyun,Kim, Eui Jung,Kim, Bum Sung,Chung, Jin Suk The Royal Society of Chemistry 2013 Chemical communications Vol.49 No.59

<P>We introduce ammonia borane, a versatile reducing agent for graphene oxide (GO) reduction in both aqueous and organic solvents; it is nontoxic and more effective than hydrazine. More interestingly, ammonia borane reduction of GO tetrahydrofuran produced higher nitrogen- and boron-doped graphene that exhibited high supercapacitor performance.</P> <P>Graphic Abstract</P><P>We introduce ammonia borane, a versatile reducing agent for graphene oxide (GO) reduction in both aqueous and organic solvents; it is nontoxic and more effective than hydrazine. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c3cc43503b'> </P>

Synthesis of highly concentrated suspension of chemically converted graphene in organic solvents: Effect of temperature on the extent of reduction and dispersibility

Viet Hung Pham,정진석,Thanh Truong Dang,Tran Viet Cuong,Seung Hyun Hur,Byung-Seon Kong,김의정 한국화학공학회 2012 Korean Journal of Chemical Engineering Vol.29 No.5

We report the effect of temperature on the extent of graphene oxide reduction by hydrazine and the dispersibility of the resulting chemically converted graphene (CCG) in polar organic solvents. The extent of graphene oxide reduction at high temperatures was only slightly higher than at low temperatures (30-50 oC), while the dispersibility of the resulting CCG in organic solvents decreased markedly with increasing temperature. The low dispersibility of CCGs prepared at high temperatures was greatly affected by reduction and influenced by the formation of an irreversible agglomerate of CCG at high temperatures. The reduction of graphene oxide at low temperatures is necessary to prepare highly dispersible CCG in organic solvents. CCG prepared at 30 oC is dispersible in N-methyl-2-pyrrolidone concentrations as high as 0.71 mg/mL. The free-standing paper made of this CCG possessed an electrical conductivity of more than 22,000 S/m, one of the highest values ever reported.

Adaptive hierarchical sliding mode control using an artificial neural network for a ballbot system with uncertainties

Hai Le Xuan,Quoc-Dong Hoang,Soon Geul Lee,Dat Pham Xuan,Hoang Tran Viet,Minh Pham Van,Hung Pham Van,Hung Pham Viet,PHAM DUC TUAN,Duc Anh Nguyen 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.2

Ballbots, which have been studied for over ten years, are under-actuated mobile robots that operate using the inverted pendulum paradigm. Controlling a ballbot poses a number of challenges, including maintaining the stable upright posture from the ground in all directions and making sure it follows the desired trajectory. External factors such as a minor change in contact surface properties or fabrication errors can affect the system's stabilization and transfer capabilities. In this study, an adaptive hierarchical sliding mode control algorithm based on an artificial neural network is developed to make the ballbot robust to external factors. The use of the proposed controller ensures system stability despite uncertainties including friction, accidental centrifugal forces and gravity that occur when the ballbot follows the reference trajectory. The system stability is guaranteed on the basis of Lyapunov theory. Control efficiency and robot stability under system uncertainties are demonstrated by numerical simulation.