| Gel with special physical-chemical properties and unique applied performance could be transformed irreversibility from konjac glucomannan(KGM) sol as it was in aqueous solution at low concentration (over0.8%). This paper centered on the physical crosslinking KGM gelation involved in the basic problems with challenging in condensed matter physics about soft substance reassembly process. Partial primary structure, influence of solvents treatment on the contents and morphology of KGM, condensed properties of KGM in aqueous solution from diluted to concentrated polysaccharides region and influence of environmental factors on the condensed properties were investigated by polymer chemical and polymer physical theories and modern testing means. The research was supported by The National Key Technology R&D Program (2007BAE42B04).KGM morphology and the influence of solution environments on KGM morphology in plant cells, in bulk and in aqueous solutions from diluted to concentrated polymer region were investigated by microscopy. The enormous KGM grains which were pure translucent crystals were located in idioblast. The chain entanglement in KGM led to irregular small squares. The Scan Electron Microscope (SEM) examination showed that there had been an increase in holes and a decrease in diameter of the holes of the KGM solution as the concentration of KGM in aqueous solution increased from0.1%to5.0%. Atomic Force Microscope (AFM) examination showed that the concentrations of KGM in aqueous solution were0.1,5.0,10.0,60.0and100.0ug/ml respectively, and the aggregates of molecules were45.50,30.01,187.91,218.99and362.46nm in width and0.14,0.17,0.49,0.99and4.66nm in height. The results showed that solvation of KGM promoted molecule elongation.The orthogonal test design was used to arrange experiments to establish optimal purification of KGM. The optimal purification technology was as follows:0.1%KGM, at temperature of80℃for15hours,90%ethanol. KGM contents ranged up to95.45%, the yielding rate of KGM was80%. KGM consisted of1â†'4linked glucose and mannose units. KGM composed of1â†'6branched chain. There were2006glucosyls and3409mannosyls. The mole ratio was1:1.7.KGM samples were characterized by ubbelodhe viscodimeter and aqueous gel permeation chromatography coupled with multi angle laser light scattering (GPC-MALLS) and refractive index detector (RID). Further determination was undertaken by combining intrinsic viscosity with GPC. The intrinsic viscosity of KGM in aqueous solution was1755.56ml/g, Huggins coefficient was0.34. Mw=877200g/ml Mn=837700g/mol Mz=1803400g/mol Mp=993200g/mol, MW/MH=1.047<Rg2Z1/2=121.9nm A2=(1.175±0.495)×10-2(mol·ml/g2),the χ1parameter was0.487; Mark Houwink relationship was as follows:[η]=5.19×10-4MMn0.90,that mean water was the good solvent. Intrinsic viscosity of KGM in aqueous solution at pH1,2,3,4and5were898.49ml/g,1511.86ml/g,1630.46ml/g,1692.91ml/g and1715.57ml/g and Huggins coefficients were0.98,0.76,0.39,0.36and0.35。Rheological measurements were carried out to discuss the fundamental problem such as contact concentration, different ranges of concentration, entanglement an network of KGM solution, sol and sol-gel transform.The overlap concentration (c*) of KGM solution was0.11%, KGM chains became congested and eventually touch each other. At the so-called overlap concentration, there were5.8chains for each cube of a volume of a KGM sphere. At c<c*, the KGM solution was close to an ideal solution. At c>0.15%, the KGM solution was pseudoplastic fluid. Rouse-Zimm model provided the correct expressions of KGM chain dynamics. The molecular mass determined by SEC-RID was decreased from7.55×105g/mol to6.35×105g/mol as the concentration of KGM in aqueous was increased from0.025mg/ml to1.0mg/l. The molecular mass fell15.9%. KGM coils would be closer with the increase in concentration, the size of KGM coils did not have a sufficient space available, the chains were overlapped.The concentration from0.15%to2.30%belonged to KGM solution, which showed a Newtonian-fluid characteristic and the exponential growth viscosity. K=4.29×e2.11C-7.96, n=0.79e256C+0.29could be used to describe the effect of concentration on the consistency coefficient and power index. The intersection of storage modulus and loss modulus for1.5%KGM aqueous solution was observed at the frequency0.8rad s-1lower than1which was suggested to mark the cohesional entanglement point of KGM chain. The Winter-Chambon method was found to be still effective in determination of the sol-gel transition. The sol-gel transition point concentration was determined to be2.33%, and the corresponding n was calculated to be0.42. Cohesional entanglement was transited to topological entanglement. Burgers model provided the correct expressions of KGM chain dynamics in sol.KGM gel was conformed at concentration was at concentration2.3%in which KGM chain formed the discontinuous local network structure. Me=4.29e-2.31C+1.53x10-7e-0.58C+1.8×105could be used to describe the effect of concentration on Me. When the concentration was increased up to5.0%, KGM chains transformed from discontinuous local network structure into a continuous network structure. The net work structure was the mechanism of KGM gelation. Reptation model was introduced to explain the network of KGM chain dynamics in gel.With increasing KGM concentration, the dynamic storage modulus (G’) and loss modulus (G") increased. The G’, G" kept decreasing with increasing the temperature until KGM chain reached Cohesional entanglement (KGM concentration1.5%), but storage modulus decreased sharply particularly in lower concentration. Since the concentration beyond1.5percent, The G’,G" decreased at first and then increased gradually. The lower concentration, the more modulus dropped. The results showed that high concentrations would cause local network structures even contiguous net work structures with higher-strength mechanics properties than entanglement. The higher concentration, the lower temperature at turning point of modulus change (from85℃drop to60℃).0.5%KGM sol would be changed to Newtonian fluid from Pseudoplastic fluid at pH to1. The dynamic modulus of5.0%KGM gel would be decreased1000times as decreasing pH to1. Small pH changes had little impact on the rheological behavior of KGM from diluted to concentration region. The chemical crosslinking reaction was produced at pH to13.Urea had no impact on the rheological properties of0.5%KGM sol and5.0%KGM gel. With increasing urea concentration from0.01to0.1mol/L, the dynamic loss modulus and storage modulus increased while the dynamic loss modulus and storage modulus decreased. The results showed that the mobility of segments in KGM coil had little impact on entanglement as cross link density was increased. Urea/KGM systems were insensitive to temperature.The dynamic modulus of KGM gel would be changed by slats which changed the charge of KMG molecule in solution. That process led to damage the network of KGM gel. Salt had little impact of entanglement density of KGM gel, but had certain effect on entanglement strength. The results showed that electrostatic attraction and volume-phase effects had effect the intermolecular interactions.In the solid state, polymer molecules are in close contact with other polymer molecules. The physics of such a system is quite different from that of the individual molecules because of collective effects. Even in the same polymer with the same chain, different aggregative states will be produced in different conditions of processing. Behavior of KGM in solvents is an important content in the research of the condensed properties of polysaccharides. The results will be of referential values for solution theory of polysaccharides. At the same time, the results will provide tech support to further development and application of KGM in the field of agriculture, food, chemical engineering, petroleum, environmental protection and national defence. |
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