Browsing by Subject "Percolation"
Now showing items 1-12 of 12
-
Conductivity percolation of carbon nanotubes (CNT) in polystyrene (PS) latex film
Authors:
Publisher and Date:(Canadian Science Publishing Nrc Research Press, 2010)In this study the effect of multiwalled carbon nanotubes (MWNT) on film formation behaviour and electrical conductivity properties of polystrene (PS) latex film was investigated by using the photon transmission technique and electrical conductivity measurements. Films were prepared by mixing PS latex with different amounts of MWNTs varying in the range between 0 and 20 wt%. After drying MWNT content films were separately annealed above the glass transition temperature (T-g) of PS ranging from 100 ...
-
Critical Exponents of Gelation and Conductivity in Polyacrylamide Gels Doped by Multiwalled Carbon Nanotubes
Authors:
Publisher and Date:(Taylor & Francis Ltd, 2010)Polyacrylamide (PAM) doped by multiwalled carbon nanotube (MWNT) gels were prepared with different amounts of MWNTs varying in the range between 0.1 and 15 wt%. The PAM-MWNT composite gels were characterized by the steady state fluorescence technique (SSF). The alternative electrical conductivity (AC) of PAM-MWNT composite gels was measured by the dielectric spectroscopy technique. Observations around the gel point t(gel) for PAM-MWNTs composite gels showed that the gel fraction exponent beta ...
-
Critical Exponents of Thermal Phase Transitions of kappa-Carrageenan in Various Salt Solutions
Authors:
Publisher and Date:(Wiley-VCH Verlag GmbH, 2009)The steady state fluorescence (SSF) technique was employed to study the phase transitions Of kappa-carrageenan in NaCl and KCl solutions. Pyranine was used as a fluorescence probe for monitoring these transitions. Scattered light I(sc) and fluorescence intensity 1 was monitored against temperature to determine transition temperatures and exponents. It was observed that transition temperatures are strongly correlated with the NaCl and KCl contents. The weight-average degree of polymerization DP(w) ...
-
Critical phenomenon during photoinitiated gelation at different temperatures: A Photo-DSC study
Authors:
Publisher and Date:(Elsevier Science, 2011)The behaviour of photoinitiated radical polymerization of an 80 wt% epoxy diacrylate (EA) and 20 wt% tripropyleneglycoldiacrylate (TPGDA) mixture with 2-mercaptothioxanthone (TX-SH) photoinitiator was studied at different temperatures by using photo-differential scanning calorimetric (Photo-DSC) technique. All photopolymerization reactions were carried out under the same conditions. It was observed that all conversion curves during gelation at different temperatures present nice sigmoidal behaviour ...
-
Electrical and optical percolations in PMMA/GNP composite films
Authors:
Publisher and Date:(Taylor & Francis Ltd, 2018)Effects of graphene nanoplatelet (GNP) addition on the electrical conductivity and optical absorbance of poly(methyl methacrylate)/graphene nanoplatelet (PMMA/GNP) composite films were studied. Optical absorbance and two point probe resistivity techniques were used to determine the variations of the optical and electrical properties of the composites respectively. Absorbance intensity A and surface resistivity R-s of the composite films were monitored as a function of GNP mass fraction (M) at room ...
-
Electrical optical and fluorescence percolations in P(VAc-co-BuA)/MWCNT composite films
Authors:
Publisher and Date:(Taylor & Francis Ltd, 2013)Effects of multiwall carbon nanotube (MWCNT) addition on the electrical conductivities optical transparencies and fluorescence emissions of poly(vinyl acetate-co-butyl acrylate) (P(VAc-co-BuA))/MWCNT composite films were studied. Optical transmission fluorescence emission and two point probe resistivity techniques were used to determine the variations of the optical fluorescence and electrical properties of the composites respectively. Transmitted photon intensity (I-tr) fluorescence emission ...
-
GELATION MECHANISMS
Authors:
Publisher and Date:(World Scientific Publ Co Pte Ltd, 2012)In this paper, we survey the gelation mechanisms for various polymeric systems which are classified by the type and the strength of the cross-linkages. These are the "irreversible" gels that are cross-linked chemically by covalent bonds and the "reversible" gels that are cross-linked physically by hydrogen or ionic bonds and by the physical entanglement of polymer chains. Some of the natural polymer gels fall into the class of physical gels, among which the red algae that has attracted attention ...
-
Gelation of PAAm-PVP composites: A fluorescence study
Authors:
Publisher and Date:(World Scientific, 2014)Hybrid hydrogels are a new class of composite materials. Polyacrylamide (PAAm) hydrogels are mainly produced by free radical crosslinking copolymerization (FCC) of AAm in the presence of N N'-methylene bis (acrylamide) (BIS) as the crosslinker. Pyranine doped PAAm-poly (N-vinyl pyrrolidone) (PVP) composite were prepared with different amounts of PVP varying in the range between 0.0015 and 0.1 gr. It was observed that pyranine molecules as a fluoroprobe bind to AAm and PVP chains upon the initiation ...
-
Percolation and Film Formation Behaviors of MWNT/PS Nanocomposites
Authors:
Publisher and Date:(Elsevier Science Bv, 2011)This study involves the investigation of film formation and electrical conductivity properties of polystrene (PS) latex/multi-walled Carbon nanotube (MWNT) composites. Films prepared from PS/MWNT mixtures with different MWNT content were separately annealed above glass transition temperature of PS. Film formation stages of PS/MWNT composites were followed by monitoring the change in transmitted light intensity I-tr. The surface conductivity of films was found to increase dramatically above 4 wt% ...
-
Phase Transitions in Pure and Hybrid Hydrogels: A Fluorescence Study
Authors:
Publisher and Date:(Wiley, 2009)Recent observations on phase transitions around the critical point showed that the critical exponents differed drastically from percolation results and classical results for pure hydrogel systems depending on monomer concentration. in addition to pure hydrogels the sol-gel phase transition during radical crosslinking copolymerization of acrylamide (AAm) and N-isopropylacrylamide (NIPA) hybrid was studied by using the steady state fluorescence (SSF) technique. NN'-methylenebis(acrylamide) (BIS) and ...
-
Polymer-Ceramic Nanocomposites
Authors:
Publisher and Date:(Spie-Int Soc Optical Engineering, 2009)Steady state fluorescence (SSF) and photon transmission (PT) techniques were used for studying film formation from TiO2 and Al2O3 covered polystyrene (PS) latex particles. These films were annealed at elevated temperatures in 10 min time intervals above glass transition (T-g) temperature of polystyrene. Fluorescence emission I-P and transmitted photon I-tr intensities were measured after each annealing step to monitor the stages of film formation. Films present dramatic increase in both I-tr and ...
-
Steady state fluorescence technique for studying phase transitions in PAAm-PNIPA mixture
Authors:
Publisher and Date:(Taylor & Francis, 2009)The steady state fluorescence (SSF) technique was used to study the sol-gel phase transition during free radical crosslinking copolymerisation of various amounts of acrylamide (AAm) and N-isopropylacrylamide (NIPA) mixtures. NN'-methylenebis (acrylamide) (BIS) and ammonium persulfate (APS) were used as crosslinker and an initiator respectively. Pyranine (8-hydroxypyrene-1 3 6-trisulfonic acid trisodium salt HPTS) was added as a fluoroprobe for monitoring the polymerisation. It was observed that ...
