Hyperbranched polyester as a crosslinker in polyurethane formation: real-time monitoring using in situ FTIR

Dhevi, D. M.,Anand Prabu, A.,Kim, K. J. Springer Science + Business Media 2016 Polymer bulletin Vol.73 No.10

<P>Hyperbranched polymers find applications in many fields such as biomedical, catalysis, commercial coatings, etc., owing to their many advantages such as ease of synthesis, more number of end functional groups, and low solution/melt viscosity. In our study, a previously unreported synthesis of A(2) + AB(2) type hyperbranched polyester (HBP) of three different generations (HBP-G1 to HBP-G3) using phenyl dichlorophosphate as a core and 2,2-dimethylol propionic acid as a monomer was carried out, and characterized using spectral, physical and thermal analyses. In situ FTIR was used to study the one-shot curing reaction between hexamethylene diisocyanate, polyethylene glycol and HBP-G3 at 60 A degrees C for two different NCO/OH ratios (1.2316 and 2.1042). Lower NCO/OH ratio (1.2316) was found to obey the second order, thereby indicating the occurrence of primary reaction between -OH and -NCO groups, whereas higher NCO/OH ratio (2.1042) follows third order due to auto-catalytic effect of urethane resulting from its reaction with excess isocyanate group. Non-isothermal curing kinetics of PU formation using in situ FTIR was accomplished to determine the percentage of urethane content formed using Factor Analysis program for the first time. Based on the above data, further curing kinetics studies were carried out at three different isothermal (70, 90, and 110 A degrees C) temperatures for lower NCO/OH ratio sample to extract its thermodynamic parameters.</P>

FTIR studies on polymorphic control of PVDF ultrathin films by heat-controlled spin coater

Dhevi, D. M.,Prabu, A. A.,Kim, K. J. Springer Science + Business Media 2016 JOURNAL OF MATERIALS SCIENCE - Vol.51 No.7

<P>The performance of organic polymer-based memory devices based on polyvinylidene fluoride (PVDF) ultrathin films depends on the extent of its ferroelectric crystalline phase content. In the present study, the changes in polymorphs of PVDF ultrathin films prepared by using heat-controlled spin coater are examined. The polymorphic changes were analyzed by using FTIR-transmission (TS) and FTIR-grazing incidence reflection-absorption spectroscopy (GIRAS) as a function of varying (i) spin-coating temperatures (SCT-30 to 80 A degrees C), (ii) spin-coating substrates (KBr, ITO and Gold) and (iii) thermal treatments [as-cast (AC) at 30 A degrees C, annealed at 130 A degrees C (AN130) and melt (200 A degrees C)-slow cooled (MSC)] conditions. Compared to MSC samples, the AC and AN130 samples exhibited higher beta-crystalline (polar, all-trans) phase along with the complete absence of alpha-crystalline (non-polar, tgtg') phase at lower SCT-30 and 40 A degrees C irrespective of the substrates used, thereby avoiding the need of high-temperature SCT conditions. Among the three substrates used, FTIR-GIRAS data obtained using ITO and Gold substrates were more favored than the FTIR-TS data obtained using KBr window due to their real-time usage as the substrate for electronic applications.</P>

Spin-Coating Temperature Induced Changes in Ferroelectric Crystallinity in Polyvinylidene Fluoride Ultrathin Films

Dhevi, Dhevagoti Manjula,Prabu, Arun Anand,Pathak, Madhvesh,Kim, Kap Jin Trans Tech Publications, Ltd. 2012 Advanced materials research Vol.584 No.-

<P>In the present study, calculated amount of polyvinylidene fluoride (PVDF) was added to a mixture of two different polar solvents and maintained under continuous stirring for overnight. The PVDF solution thus obtained was spin-coated over divergent substrates like KBr and gold coated glass substrates at 80 oC. The spin-coated samples were further exposed to varying thermal conditions such as as-cast (AC), annealed at 130 °C (AN) and melt (200 °C)-slow cooled (MSC) for a period of time. FTIR spectroscopic data obtained from this study was found to be quite useful in analyzing the changes in absorption intensity of crystalline phase changes as a function of varying substrate and heat treatment conditions. Aβ,γ,α/A1073 ratio was observed to be favorable for AN samples when compared to that of AC and MSC samples, and among the substrates, gold is more preferable due to its real-time usage as a substrate in electronic device applications.</P>

Deterioration in mechanical properties of glass fiber-reinforced nylon 6,6 composites by aqueous calcium chloride mixture solutions

Dhevi, D. Manjula,Choi, Chang Woo,Prabu, A. Anand,Kim, Kap Jin Wiley Subscription Services, Inc., A Wiley Company 2009 Polymer composites Vol.30 No.4

<P>In this article, nylon 6,6 (NY66) and glass fiber-(30 wt%) reinforced NY66 (GFNY66) specimens were immersed in various aqueous calcium chloride (aq. CaCl<SUB>2</SUB>) mixture solutions at different thermal conditions for varying intervals of time, and analyzed using attenuated total reflection-infrared (ATR-IR) spectroscopy, inductively coupled plasma (ICP), energy dispersive X-ray (EDX), gel permeation chromatography (GPC), and mechanical studies. ICP data revealed increasing concentration of absorbed Ca<SUP>2+</SUP> ions with increasing immersion time resulting in disruption of intra- and intermolecular H-bonding as confirmed using ATR-IR results. From EDX data, the ratio of Ca<SUP>2+</SUP> and Cl<SUP>−</SUP> ions absorbed by NY66 was calculated and found to follow its stoichiometric equivalence. GPC data exhibited less reduction in M<SUB>n</SUB> and M<SUB>w</SUB> for aq. CaCl<SUB>2</SUB>-treated NY66 specimens suggesting the absence of any significant chemical degradation, but the occurrence of only physical changes involving H-bond breakage and the formation of new C&n.dbond;O···Ca<SUP>2+</SUP> dative bond in NY66 matrix. The mechanical properties of GFNY66 samples treated with various types of aq. CaCl<SUB>2</SUB> solutions exhibited pronounced deterioration, possibly due to the interfacial failure between glass fiber and NY66 matrix. The results obtained from this study were quite useful toward understanding the degradation mechanism in NY66 and GFNY66 caused by various aq. CaCl<SUB>2</SUB> mixture solutions, and will be helpful in improving the mechanical properties of recycled NY66. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers</P>

Efficacy of snakehead fish (Channa striatus ) in subjects with allergic rhinitis: a randomized controlled trial

Bathma Dhevi Susibalan,Baharudin Abdullah,Norhafiza Mat Lazim,Azidah Abdul Kadir 경희대학교 융합한의과학연구소 2018 Oriental Pharmacy and Experimental Medicine Vol.18 No.3

Allergic rhinitis is a prevailing chronic infl ammatory respiratory disorder that aff ects 10–30% of the population globally. Channa striatus (Channa) is a snakehead, freshwater fi sh that has been used traditionally to enhance wound healing and relief post-operative pain. This study evaluates the effi cacy of oral Channa extract on allergic rhinitis subjects on total nasal symptom score and serum immunoglobulin E (Ig E). A randomized, double-blind, placebo-controlled trial was conducted by comparing the oral Channa extract 500 mg/day and placebo among allergic rhinitis subjects for a 6-week intervention period. Subjects aged 18–50 years old, diagnosed with allergic rhinitis based on total symptoms score, naso-endoscopy fi ndings, and positive skin prick test were included in this trial. All subjects were treated with antihistamine (levocetrizine) and local corticosteroid nasal spray (fl uticasone furoate nasal spray). Laboratory-based blood tests were used as safety measures. A total of 70 subjects were randomized. Channa group showed signifi cant improvement in nasal blockage ( p < 0.05), nasal itchiness ( p < 0.05), eye itchiness ( p < 0.05) and general symptoms ( p < 0.05) compared to the placebo groups. Serum Ig E were signifi cantly lowered in Channa group compared to placebo ( p < 0.001). No signifi cant diff erences were found between the groups in terms of nasal discharge, sneezing, palate itchiness, and smell score. No serious adverse events were reported. In conclusion, Channa has a benefi cial role in improving nasal symptoms and reduction in serum Ig E in allergic rhinitis subjects.

Electrospun Polyvinylidene Fluoride-Polyoctafluoropentyl Acrylate- Hydroxyapatite Blend Based Piezoelectric Pressure Sensors

Ponnan Sathiyanathan,Dhevagoti Manjula Dhevi,Arun Anand Prabu,김갑진 한국고분자학회 2019 Macromolecular Research Vol.27 No.8

In this study, neat polyvinylidene fluoride (PVDF), PVDF/polyoctafluoropentyl acrylate (PFA, 90/10 w/w) and PVDF-PFA/hydroxyapatite (HAP, 0 to 20 wt% HAP w.r.t. PVDF-PFA content) were electrospun under controlled conditions, and studied for their piezo-responsive behaviours as a function of nanoweb stacking arrangement (constructive and destructive) and folding architectures (simple, series and parallel connection of electrodes between each folding). Influence of varying HAP content (0, 3, 7, 10, and 20 wt%) on the molecular orientation of CH2-CF2 dipoles in PVDF-PFA/HAP blends were investigated using FTIR, XRD and SEM analysis. Quantitative analysis showed increased β-crystalline content for the 7 wt% HAP sample. From the peak-to-peak output voltage, 7 wt% HAP sample exhibited significantly higher output voltage (Vp-p = 1.21 V) compared to neat PVDF-PFA sample (Vp-p = 0.46 V). Overall, the combinative effect of HAP addition and folding played a vital role in improving the piezoelectric output signals of PVDF-PFA/HAP, which signifies the importance of this study.

Effect of Thermal Cycling on the Ferroelectric Characteristics of Vinylidene Fluoride-Trifluoroethylene Copolymer Thin Films

Sathiyanathan, P.,Manjula Dhevi, Dhevagoti,Prabu, Arun Anand,Kim, Kap Jin Trans Tech Publications, Ltd. 2012 Advanced materials research Vol.584 No.-

<P>Thin films of polyvinylidene (PVDF) and its copolymers containing 50 to 30 mole % of trifluoroethylene (TrFE) demonstrate rapid reversal of polarization under applied electric field, and can be used as ferroelectric materials in non-volatile memory devices. In this study, Fourier-transform infrared transmission (FTIR-TS) and grazing incident reflection absorption (FTIR-GIRAS) spectroscopy techniques were used to examine the changes in Curie transition temperature (Tc), chain and dipole orientation in selected VDF copolymer spun-cast films as a subjected to a reversible thermal-cycling treatment. A reversible solid-to-solid β-crystalline phase transition with thermal hysteresis and a favorable C-F dipole orientation along the electric field direction were observed for the sample subjected to thermal-cycling below its melting point (Tm). An irreversible β-crystalline phase transition with unfavorable C-F dipole orientation was observed for the sample treated to heating-cooling cycle above Tm. The results are reported in detail here.</P>