在本研究中，利用自由基聚合法合成PNIPAAm [Poly(N-isopropyl acrylamide]水膠及溶液，其中水膠以NMBA (N,N′-methylene-bis-acrylamide)做為交聯劑。將應力應變實驗結果利用Slip link模型來分析水膠中物理糾纏與化學交聯密度；由膨潤性質及應力應變實驗結果計算水膠的有效交聯密度(ve)，以橡膠彈性統計熱力學模型估算相關長度(ξest)。使用動態雷射光散射儀(DLS)測量PNIPAAm水膠及溶液的相關長度(ξDLS)，並與熱力學估算相關長度(ξest)之結果做比較。以可控溫型紫外光可見光分光光度計測量水膠及溶液在不同升溫速率(Vheat)下，從30到45℃時透光度(Tr)隨時間的變化，以臨界點求得無限慢升溫速率下的相變化溫度(Ts,0; lower critical solution temperature)；以初始時期的透光度(Tr)隨時間的變化求得spinodal decomposition初期的緩和時間(τ∞)。
NIPAAm與NMBA進料比例(CNIPAAm/CNMBA)越高的水膠，平衡澎潤時高分子體積分率(ν2,s)越高，彈性模數(G)增加。隨著進料比例增加，物理纏結相對增加，產生的抗力會上升；但水膠中物理纏結及化學交聯的相對比例，隨進料比例改變不大。水膠中高分子體積分率越高，有效交聯密度(ve)上升，交互作用參數(χ)增加，交聯點間分子量(Mc)越大，相關長度(ξest)下降。由DLS所測量的相關長度(ξDLS)大於理論估算的相關長度(ξest)，可能是因為真實的水膠內有許多末端鏈及物理纏結等造成水膠不均勻分布，真實的水膠相關長度會較熱力學計算(假設affine network)的相關長度大。
水膠和溶液相變化前的相關長度(ξDLS)對高分子體積分率冪次關係中的指數，溶液(-0.399)大於水膠(-0.301)，相關長度絕對值，溶液小於水膠。水膠及溶液中高分子體積分率增加，相變化溫度會越低，且水膠高於溶液；水膠交聯程度越高，相變化溫度越高；水膠及溶液的相關長度(ξDLS)增加，相變化溫度亦增加，兩者近似線性關係；以相變化溫度與高分子體積分率關係，計算水膠及溶液相變化的莫耳焓，溶液高於水膠。水膠和溶液緩和時間對高分子體積分率冪次關係中的指數，溶液(-0.580)亦大於水膠(-0.338)，緩和時間絕對值，溶液亦高於水膠。緩和時間與相關長度(ξDLS)的冪次關係中的指數，水膠(1.057)與溶液(1.143)相當接近，緩和時間與相關長度接近一次方線性關係。水膠因為交聯網狀結構的限制，相關長度(ξDLS)及緩和時間受高分子體積分率影響較溶液小。水膠相變化所需的能量小於溶液，水膠的相變化速率較溶液快。水膠及溶液緩和時間對相變化推動溫度(外界溫度與相變化溫度差)冪次關係中的指數，水膠(1.419)稍微偏離Ising model所預測的結果(1.28)，而溶液(7.629)偏離較大，可能是因為分子間作用力造成。

PNIPAAm [Poly(N-isopropyl acrylamide] hydrogels and solutions were prepared by free radical polymerization with NMBA (N,N′-methylene-bis-acrylamide) crosslinker. The stress-strain data of hydrogels fitted with the slip-link model was used to calculate the densities of chemical crosslink and the densities of physical entanglement for hydrogels. We calculated the effective crosslink densities (ve) by swelling test data and stress-strain data. The correlation lengths (ξest) of hydrogels were calculated from the thermodynamic equilibrium equation. We used dynamic laser light scattering to measure the dynamic correlation lengths (ξDLS) of hydrogels and solutions, and compared them with the estimated correlation lengths of hydrogels. We used UV-VIS spectrophotometer to measure the transmittance (Tr) versus time with various heating rates from 30 to 45℃ for hydrogels and solutions. The phase transition temperatures (Ts,0; i.e., lower critical solution temperature) and the relaxation times (τ∞) of early stage spinodal decomposition are determined from data of transmittance versus time in the critical point and the initial stage, respectively.
The polymer volume fractions (ν2) and elastic modules (G) are increased with increasing the feed ratio of NIPAAm to NMBA in hydrogels. The physical entanglements and chemical crosslinks are increased with increasing the feed ratio. The ratios of physical entanglement to chemical crosslink do not vary much with feed ratios. The effective crosslink densities, Flory-Huggins interaction parameters between crosslinked polymer and water (χ) and molecular weights between crosslinked points (Mc) are increased with increasing the polymer volume fractions. The estimated correlation lengths (ξest) of hydrogels were calculated from ν2 and Mc, which were decreased with increasing the polymer volume fractions. The dynamic correlation lengths (ξDLS) are bigger than the estimated correlation lengths for hydrogels. This difference can be attributed to the inhomogeneity that caused by the end chains or physical entanglements in the hydrogels.
The exponent values of power relations between dynamic correlation lengths (ξDLS) and polymer volume fractions for hydrogel and solution are -0.301 and -0.399, respectively. However, the dynamic correlation lengths for hydrogels are bigger than solutions. The phase transition temperatures are decreased with increasing the polymer volume fractions in two kinds of samples. The phase transition temperatures for hydrogels are higher than solutions. The phase transition temperatures are increased with increasing the chemical crosslink for hydrogels. The phase transition temperatures for both are linearly increased with increasing the dynamic correlation lengths. The relation between phase transition temperatures and polymer volume fractions can be used to calculate the enthalpies of phase transition of hydrogel and solution, in which the enthalpy of hydrogel is larger than solution. The exponent values of power relations between relaxation times and polymer volume fractions for hydrogel and solution are -0.338 and -0.580, respectively. However, the relaxation times for hydrogels are smaller than solutions. The exponent values of power relations between relaxation times and dynamic correlation lengths (ξDLS) for hydrogel and solution are 1.057 and 1.143, respectively, with very minor difference. The dynamic correlation lengths (ξDLS) and phase transition rates of hydrogels are less affect by polymer volume fractions than solutions, because of the restriction by crosslink networks of hydrogels. The phase transition rates of hydrogels are faster than solutions, because the energies needed in causing phase transition of hydrogels are lower than solutions. The exponent values of power relations between relaxation times and reduced temperature for hydrogel and solution are 1.419 and 7.629, respectively, whereas solution behavior is deviated far away from Ising model with an exponent of 1.28.

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