Xanthan gum (XG) is widely used in cosmetic and pharmaceutic products (creams, pastes) and in oil industry (drilling fluids) as a stabilizing and/or thickening agent. In literature, its rheological behavior is mainly presented as that of a shear-thinning or a yield stress fluid. Here, in order to clarify this rheological behavior, we study in detail the flow characteristics during continued flow under given conditions (i.e., controlled stress) for a mass concentration ranging from 0.2 to 5%. We are thus able to identify the apparent flow curve of the material after a short flow duration and the flow curve in steady state (i.e., after a long flow duration). The validity of this flow curve, determined from standard rheometry, is confirmed by magnetic resonance velocimetry. These materials start to exhibit a yield stress behavior beyond some critical xanthan or salt concentration. In that case, a significant increase (by a factor up to 5) of the apparent viscosity is observed during flow in some range of stresses, before reaching a steady state. This original rheopectic effect might be due, after some time of flow associated with deformation and reconfiguration of the XG molecules, to the progressive formation of intermolecular links such as hydrogen bonds and/or intermolecular association due to acetate residues.

黄原胶 (XG) 广泛用于化妆品和医药产品（膏霜、糊剂）和石油工业（钻井液）中作为稳定剂和/或增稠剂。在文献中，其流变行为主要表现为剪切稀化或屈服应力流体。在这里，为了阐明这种流变行为，我们详细研究了在质量浓度范围为 0.2% 到 5% 的给定条件（即受控应力）下连续流动过程中的流动特性。因此，我们能够确定材料在短时间流动后的表观流动曲线和稳定状态下（即在长时间流动后）的流动曲线。由标准流变测定法确定的该流动曲线的有效性由磁共振测速法证实。这些材料开始表现出超出某些临界黄原胶或盐浓度的屈服应力行为。在这种情况下，在达到稳定状态之前，在一定应力范围内的流动过程中观察到表观粘度显着增加（最多 5 倍）。这种原始的流变效应可能是由于在与 XG 分子的变形和重新配置相关的流动一段时间后，逐渐形成分子间连接，例如氢键和/或由于乙酸盐残基引起的分子间缔合。