本研究中裡利用不同含量的水吸附在孔洞材料中,改變溫度條件,測量隨著磁場頻率變化之自旋晶格弛豫速率(R1),再搭配分子運動模型去分析不同含量水在孔洞中的水分子的運動情況。 在自旋晶格弛豫速率(R1)量測部分,實驗結果顯示:在同一個溫度條件下,R1弛豫速率的趨勢隨著磁場頻率變大R1弛豫速率變小。隨著溫度下降,R1弛豫速率上升。另外含水量越低弛豫速率也較大。第二部分為孔洞中水分子運動的分析,此系統當中主要有七個參數:大孔洞的快速運動(fast motion)及慢速運動(slow motion)、小孔洞的快速運動、秩序性參數(order parameter)、自旋耦合常數(spin dipolar coupling)、各運動區域的分佈比例。分析結果顯示:分布情況而言,由於毛細現象,因此水分子在吸附過程中優先將小孔洞先填滿,因此在不同含量水的情況下,大孔洞表面所佔比例大致相同,隨著溫度降低佔有比例也降低,但是大孔洞中間部分會隨含水量及溫度降低有部分結冰的現象,變化較明顯。運動情況而言,小孔洞運動最慢,大孔洞中間部分運動最快,大孔洞表面運動次之。第三部分為相轉變溫度的探討,所在環境的不同其相轉變溫度(Ts)也不同。在擁擠的環境下,因為氫鍵網扭曲造成相轉變溫度(Ts)隨之下降。孔徑大小也會影響其相轉變溫度。 因此,我們利用了快速場循環磁共振儀獲得弛豫速率的分布曲線再搭配分子運動模型,進一步分析模擬求得所需的參數,以便探討水分子在局限空間中的動態學、分布狀況及相轉變。
FFC (Fast Field Cycling)NMR relaxometry is a very powerful tool to investigate the molecular dynamic at low frequency (0.01-40MHz) and study the slow molecular motions.Relaxation used in this present study has more advantages over mechanical field cycling.The important applications of FFC NMR includes proteins ,liquids which confined in porous materials ,and polymers. The relaxation rate of bulk and confined sample are different at low frequency region (0.01-40MHz). In this study ,nuclear magnetic relaxation dispersion (NMRD) is utilized to investigate the H2O molecular dynamic with 5% , 10% and 20% content in H-ZSM-5 at the temperature range of 208K and 298K. We got some molecular dynamic parameters by molecular dynamic fitting. According to NMRD profile , We found that the relaxation rate increases gradually with the decreasing frequencies and then increases with the decreaseing temperature. According to the fitting data ,we can get some message about dynamic and distribution of water which confined in the pore material .In addition , we found that phase transition temperature has something to do with water where in big or small pore.