Newell H E, Buckton G, Butler D A, Thielmann F, Williams D R
Department of Pharmaceutics, School of Pharmacy, University of London, 29-39 Brunswick Square, WC1N 1AX, London, UK.
Int J Pharm. 2001 Apr 17;217(1-2):45-56. doi: 10.1016/s0378-5173(01)00589-0.
The purpose of this study was to assess the effect of relative humidity (RH) on the surface energy of amorphous lactose. Two samples of amorphous lactose were investigated; a spray dried 100% amorphous material and a ball milled sample of crystalline lactose. The milled sample had less than 1% amorphous content by mass, but on investigation at 0% RH, yielded surface energies comparable to those obtained from the 100% amorphous material, indicating that the surface was amorphous. The effect of increasing humidity was to reduce the dispersive surface energy of the two samples from 36.0 +/- 0.14 and 41.6 +/- 1.4 mJ m(-2) at 0% RH for the spray dried and milled samples respectively, to a value comparable to that obtained for the crystalline alpha-lactose monohydrate of 31.3 +/- 0.41 mJ m(-2). The change in surface energy due to water sorption was only reversible up to 20% RH; after exposure to higher RH values subsequent drying did not result in a return to the original surface energy of the amorphous form. This shows that the surface is reorganising as the glass transition temperature (Tg) is reduced, even though the sample has not collapsed or crystallised. It was possible to follow the collapse behaviour in the column with ease, using a number of different methods.
本研究的目的是评估相对湿度（RH）对无定形乳糖表面能的影响。研究了两种无定形乳糖样品；一种喷雾干燥的100%无定形材料和一种球磨的结晶乳糖样品。球磨样品的无定形含量按质量计小于1%，但在0%RH下进行研究时，其表面能与从100%无定形材料获得的表面能相当，这表明其表面是无定形的。湿度增加的影响是将两种样品的分散表面能分别从喷雾干燥样品和球磨样品在0%RH时的36.0±0.14和41.6±1.4 mJ m(-2)降低到与结晶α-乳糖一水合物所获得的31.3±0.41 mJ m(-2)相当的值。由于水吸附导致的表面能变化在RH高达20%时才是可逆的；在暴露于更高的RH值后，随后的干燥并未使无定形形式恢复到原始表面能。这表明即使样品没有塌陷或结晶，随着玻璃化转变温度（Tg）降低，表面也在重新组织。使用多种不同方法可以轻松跟踪柱中的塌陷行为。
