Rheometer for rapidly measuring small quantity samples

#The present invention relates to apparatus and methods for measuring physical properties of samples when subjected to an external shear force.

#Producing materials having specific required properties is steadily gaining in importance and, hence, the field of combinatorial chemistry, which generally refers to methods for creating collections of diverse materials or compounds, commonly known as libraries, is steadily increasing and has revolutionized the process of drug discovery. Combinatorial chemistry enables researchers to rapidly discover and optimize useful materials, such as polymers, superconductors, magnetic materials, etc. In order to record the various properties of the materials obtained by combinatorial chemistry, it is necessary to precisely and efficiently determine the characteristics of the materials, preferably under varying environmental conditions. One important and useful characteristic is the behavior of a material, in particular of a polymer, when exposed to an externally-applied shear force. Instruments for measuring the response of fluids to applied shear are generally referred to as rheological instruments, which may be subdivided into indexers and rheometers. Indexers measure a quantity which is correlated with the rheological characteristics, but which is difficult to analyze in terms of intrinsic material properties. Although indexers can be assembled rapidly from commercially available components, the results of measurements carried out by means of such indexers are difficult to relate to results of measurements from other indexers, or to intrinsic material properties, without extensive calibration.

#Rheometers, on the other hand, measure intrinsic material characteristics, giving them broad applicability. Such generality, however, comes at a price due to design costs and complexity which are dictated primarily by the need for well-defined static and dynamic test conditions. Moreover, these known rheometers require fairly large quantities of sample in the order of 500 mg so as to obtain the required accuracy in analyzing the samples. Such large quantity samples, however, are usually not provided by combinatorial synthesizing methods in which, generally, a large amount of differing samples of small quantity are produced.

#FIG. 1 is a schematic perspective view of a translational embodiment of the miniature rheometer according to the present invention.

#FIGS. 2a-2c are schematic top views of actuator elements shown in FIG. 1.

#FIG. 3 is a schematic perspective view of a rotational embodiment of the miniature rheometer according to the present invention.

#With reference to FIGS. 1 and 2, a translational embodiment, i.e. an embodiment that produces a translational displacement between a top surface and a bottom surface of a sample, of the miniature rheometer according to the present invention will now be described in detail.

#In FIG. 1, merely a portion of the translational embodiment of the miniature rheometer of the present invention is shown. A moving plate 102 is mounted on a shaft 101. Another plate 100, which will also be referred to as the “fixed plate” even though this plate may be movable, is arranged parallel to the moving plate 102. Plates 100 and 102 have surfaces which are arranged in an opposed relationship so as to be parallel to each other. The geometrical structure as well as the dimensions of the respective surfaces are selected so as to result in a desired configuration. Although the plates 100 and 102 are shown as circular elements, any other geometrical structure, such as squares or rectangles, etc., may be used for the surfaces of plates 100 and 102. Plate 100 is also mounted on a shaft 103. Preferably, the shafts 101 and 103 are made of a rigid, thermally insulating material. However, any appropriate material may be used, and in some cases electrical and/or thermal conductivity of portions of the shaft 101 and 103 may be desirable. Shaft 101 is attached to an actuating element 104, which comprises a metal foil 105 which is of a rectangular shape. On at least one side of the metal foil 105, a plate of piezoelectric material 106 is attached. In this embodiment two piezoelectric plates 106 are used with the metal foil 105, however, it is also possible to use merely one piezoelectric plate on one surface of the metal foil 105. Moreover, two or more piezoelectric plates may be used in accordance with design requirements. Actuating element 104 is attached to shaft 101, preferably in a non-permanent manner, e.g. by providing a slit for receiving the actuating element 104. This permits the use of disposable plates, which in turn facilitates measurements of samples that are difficult to remove from the plates. The actuating element 104 is further attached to a mechanical assembly, which may be provided in the form of clamping blocks 107 which comprise slits for receiving end portions of the actuating element 104. A wiring assembly for applying a voltage to the piezoelectric plates 106 is also provided, but is not shown in FIG. 1. Depending on the crystallographic orientation of the piezoelectric plates 106, metal foil 105 may serve as a common electrode for applying a desired voltage to the plates 106. Alternatively, metal foil 105 may be covered by a thin, electrically-insulating layer on the middle portion, where the piezoelectric plates 106 cover the metal foil so that a voltage may be applied to the piezoelectric plates 106 by means of the electrically conductive end portions of the metal foil 105, which are clamped in place by a clamping blocks 107, which then preferably may be made of an electrically conductive material so as to serve as electrodes.

#In this embodiment, the assembly regarding the fixed plate 100 is identical to the structure referring to moving plate 102, i.e. shaft 103 is attached to an actuating element 108 comprising a metal foil 109 with piezoelectric plates 110 on either side. Clamping blocks 111 are provided in order to clamp the actuating element 108 in place. Regarding electrical connections to the piezoelectric plates 110, the wiring is configured in an analogous manner as previously described with reference to plates 106.