A study of the gelation mechanism of poly(vinyl alcohol) in aqueous solution by high-resolution solid-state 13C NMR spectroscopy

Kobayashi, Masatoshi; Kanekiyo, Masahito; Ando, Isao; Amiya, Shigetoshi

doi:10.1016/s0966-7822(98)00031-8

Cited by 13 publications

(9 citation statements)

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“…Since the AG interfered with the hydrogen bonds in PVA, a higher AG content consequently led to a lower cross-linking density and chain entanglement. 37 The lower cross-linking density allows the PBS solution to penetrate the hydrogel and increase the swelling degree. 42 Additionally, a lower AG fraction corresponded to a higher PVA content, which then led to a lower porosity.…”

Section: Resultsmentioning

confidence: 99%

Physicochemical Characteristics and Antibacterial Activities of Freeze-Thawed Polyvinyl Alcohol/Andrographolide Hydrogels

et al. 2023

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Andrographolide (AG) is one of the compounds in Andrographis paniculata, which has a high antibacterial activity. This paper reports the freeze–thaw method’s use to synthesize polyvinyl alcohol (PVA) hydrogels loaded with AG and its characterization. From the morphological examination, the porosity of the PVA/AG hydrogel was found to increase with the increasing AG concentration. The swelling degree test revealed that the hydrogels’ maximum swelling degrees were generally greater than 100%. The composite hydrogel with the highest fraction of andrographolide (PAG-4) showed greater weight loss than the hydrogel without AG (PAG-0). The molecular interaction between PVA and AG resulted in the narrowing of the band attributed to the O–H and CO stretching bonds and the emergence of an amorphous domain in the composite hydrogels. The loading of AG disrupted the formation of hydroxyl groups in PVA and interrupted the cross-linking between PVA chains, which lead to the decrease of the compression strength and the crystallinity increased with increasing AG. The antibacterial activity of the composite hydrogel increased with increasing AG. The PAG-4 hydrogel had the highest antibacterial activity of 37.9 ± 4.6b %. Therefore, the PVA/AG hydrogel has the potential to be used as an antibacterial device.

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Section: Resultsmentioning

confidence: 99%

Physicochemical Characteristics and Antibacterial Activities of Freeze-Thawed Polyvinyl Alcohol/Andrographolide Hydrogels

et al. 2023

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“…Measured values of thermal conductivity k of the PVOH‐Ag‐Bi 2 Se 3 ‐MWCNT flexible films as function of temperature were quite scattered and varied in the range 160–450 W m −1 K −1 in the temperature range 120–300 K (Figure 9b, inset), which is below the glass transition temperature of the PVOH. Scatter of k may be related to the PVOH gelation process, occurring at ≈230 K. [ 32 ] As a result, the calculated ZT of the PVOH‐Ag‐Bi 2 Se 3 ‐MWCNT hybrid networks in the temperature region 120–300 K varied between 0.2 × 10 −6 and 0.5 × 10 −6 with a tendency of slight increase with the increase of temperature. However, at the temperatures reaching the glass transition point of the PVOH (≈315 K), [ 17 ] the thermal conductivity of the PVOH‐Ag‐Bi 2 Se 3 ‐MWCNT samples strongly decreased down to ≈45 W m −1 K −1 , resulting in an order of magnitude increase of the ZT up to ≈1.6 × 10 −6 at 335 K (Figure 9b), pointing at optimal operation conditions for the PVOH‐Ag‐Bi 2 Se 3 ‐MWCNT thermoelectric films may be above the PVOH glass transition point.…”

Section: Resultsmentioning

confidence: 99%

Highly Efficient Flexible n‐Type Thermoelectric Films Formed by Encapsulation of Bi₂Se₃‐MWCNT Hybrid Networks in Polyvinyl Alcohol

Buks

Andzane

Bugovecka

et al. 2022

Adv Materials Inter

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where S is the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature, and κ is the thermal conductivity. Having both n-and p-type TE materials is an essential requirement for building an efficient TE device. [3] So far the use of organic-inorganic nanocomposites, where electrically conductive p-or n-type polymer is used as a matrix for supporting a network of carbon nanotubes (CNTs) and/or inorganic TE nanostructures as flakes, nanoplates, or nanowires has shown the greatest potential for engineering efficient flexible TE devices. [4] CNTs have been reported to be one of the most promising components for producing p-type flexible TE nanocomposites. [5][6][7][8][9] However, application of CNTs in n-type TE composites is complicated due to necessity of CNTs pretreatment (annealing under high vacuum) for oxygen desorption and transition of their conductivity type from p-type (arising from extrinsically induced by the adsorbed oxygen hole-like concentration [10] ) to n-type, and further isolation from ambient environment (air) to prevent oxygen adsorption. This significantly complicates the practical use of n-type CNTs in ambient conditions (air). Another drawback of n-type conductive polymers and their based composites is poor stability in air, resulting in decrease of electrical conductivity by orders of magnitude when exposed to air even for a short period of time. [10] The use of organic-inorganic nanocomposites has shown the greatest potential for engineering efficient flexible thermoelectric devices. In this work, a novel approach of encapsulation of as-grown bismuth selenide-multiwalled carbon nanotubes (Bi 2 Se 3 -MWCNT) hybrid network in polyvinyl alcohol for fabrication of n-type flexible thermoelectric films is demonstrated as a successful alternative to the mechanically mixed counterparts. The developed stable flexible n-type thermoelectric material has a Seebeck coefficient and power factor at room temperature as high as −85 μV K −1 and 0.4 μW m −1 K −2 , and figure-of-merit, exceeding the value shown by the mixed counterpart by ≈2 orders of magnitude, while requiring 3-4 times less inorganic material in comparison with mixed composites. Charge carrier transport mechanisms and contribution of Bi 2 Se 3 and MWCNT components of not encapsulated and encapsulated hybrid networks to the total Seebeck coefficient, electrical conductance, and power factor are studied. In addition, the fabricated flexible thermoelectric films show good environmental stability at relative humidity levels up to 60%, as well as great mechanical and electrical stability with the increase of resistance within 0.5% and deviations of the Seebeck coefficient within 2% from the initial value during the 100 repetitive bending cycles.

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“…When gelatin/PVA = 8:2, the contact angle decreases from 65 • to 33 • in about 105 s, while the opposite concentration, gelatin/PVA = 2:8, has the contact angle reduced from 65 • to 40 • in 150 s. The pure PVA is around the same variation of contact angle (55.3 • to 40.67 • in 150 s) close to that of the sample gelatin/PVA = 2:8. It seems that pure PVA, or PVA with a small amount of added gelatin, can sustain longer water dissolution as compared to the sample with a higher content of gelatin [53][54][55][56][57].…”

Section: Contact Anglementioning

confidence: 99%

Fabrication of Gelatin Nanofibers by Electrospinning—Mixture of Gelatin and Polyvinyl Alcohol

Chang

et al. 2022

Polymers

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Gelatin, one of the most abundant, naturally derived biomacromolecules from collagen, is widely applicable in food additives, cosmetic ingredients, drug formulation, and wound dressing based on their non-toxicity and biodegradability. In parallel, polyvinyl alcohol (PVA), a synthetic polymer, has been commonly applied as a thickening agent for coating processes in aqueous systems and a major component in healthcare products for cartilage replacements, eye lubrication, and contact lenses. In this study, a new type of mixed hydrogel nanofiber was fabricated from gelatin and polyvinyl alcohol by electrospinning under a feasible range of polymer compositions. To determine the optimal composition of gelatin and polyvinyl alcohol in nanofiber fabrication, several key physicochemical properties of mixed polymer solutions such as viscosity, surface tension, pH, and electrical conductance were thoroughly characterized by a viscometer, surface tensiometer, water analyzer, and carbon electron probe. Moreover, the molecular structures of polymeric chains within mixed hydrogel nanofibers were investigated with Fourier-transform infrared spectroscopy. The morphologies and surface elemental compositions of the mixed hydrogel nanofibers were examined by the scanning electron microscope and energy-dispersive X-ray spectroscopy, respectively. The measurement of water contact angles was performed for measuring the hydrophilicity of nanofiber surfaces. Most importantly, the potential cytotoxicity of the electrospun nanofibers was evaluated by the in vitro culture of 3T3 fibroblasts. Through our extensive study, it was found that a PVA-rich solution (a volumetric ratio of gelatin/polyvinyl alcohol <1) would be superior for the efficient production of mixed hydrogel nanofibers by electrospinning techniques. This result is due to the appropriate balance between the higher viscosity (~420–~4300 10−2 poise) and slightly lower surface tension (~35.12–~32.68 mN/m2) of the mixed polymer solution. The regression on the viscosity data also found a good fit by the Lederer–Rougier’s model for a binary mixture. For the hydrophilicity of nanofibers, the numerical analysis estimates that the value of interfacial energy for the water contact on nanofibers is around ~−0.028 to ~−0.059 J/m2.

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A study of the gelation mechanism of poly(vinyl alcohol) in aqueous solution by high-resolution solid-state 13C NMR spectroscopy

Cited by 13 publications

References 0 publications

Physicochemical Characteristics and Antibacterial Activities of Freeze-Thawed Polyvinyl Alcohol/Andrographolide Hydrogels

Physicochemical Characteristics and Antibacterial Activities of Freeze-Thawed Polyvinyl Alcohol/Andrographolide Hydrogels

Highly Efficient Flexible n‐Type Thermoelectric Films Formed by Encapsulation of Bi₂Se₃‐MWCNT Hybrid Networks in Polyvinyl Alcohol

Fabrication of Gelatin Nanofibers by Electrospinning—Mixture of Gelatin and Polyvinyl Alcohol

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A study of the gelation mechanism of poly(vinyl alcohol) in aqueous solution by high-resolution solid-state 13C NMR spectroscopy

Cited by 13 publications

References 0 publications

Physicochemical Characteristics and Antibacterial Activities of Freeze-Thawed Polyvinyl Alcohol/Andrographolide Hydrogels

Physicochemical Characteristics and Antibacterial Activities of Freeze-Thawed Polyvinyl Alcohol/Andrographolide Hydrogels

Highly Efficient Flexible n‐Type Thermoelectric Films Formed by Encapsulation of Bi2Se3‐MWCNT Hybrid Networks in Polyvinyl Alcohol

Fabrication of Gelatin Nanofibers by Electrospinning—Mixture of Gelatin and Polyvinyl Alcohol

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Highly Efficient Flexible n‐Type Thermoelectric Films Formed by Encapsulation of Bi₂Se₃‐MWCNT Hybrid Networks in Polyvinyl Alcohol