Compact, high-quality instrument for analyzing wettability and spreadability of materials on the skin
Characterizing the shape of a drop of water on a surface and determining its contact angle is a well-known method to analyze wettability, skin’s free surface energy, its tension and its hydrophilic/hydrophobic properties.Wettability is the ability of a liquid to maintain contact with a solid surface. Wettability can be wanted or not (repellence or spreadability).
When a defined droplet is applied to a solid medium (here: skin), the liquid forms a certain shape (drop shape). The point at which the skin, liquid and air meet determines the contact angle.The relationship between the contact angle, the skin surface free energy, the liquid surface tension and the interfacial tension between skin and liquid is defined by Young’s equation:
γS = γL cosθ + γSL
θ: Contact angle
γS: Surface free energy of the solid
γL: Surface tension of the liquid
γSL: Interfacial tension between solid and liquid
The larger the contact angle the lower the wettability, the lower the contact angle the better the wettability. In literature the relation between wettability of a substance and contact angle are defined as follows:
|small||skin’s free energy||large|
With the Drop Angle Meter, the inner forearm is placed on a comfortable rest, which can be moved vertically and tilted in order to have the skin surface where the drop is applied to absolutely levelled to prevent the water from running or disintegrating. The compact system features a very uniform diffuse LED light source and a high-resolution camera, which takes the macro image of the drop on the skin from the side, which is then automatically analyzed in the software. All data, images, and even videos are saved in the database and can conveniently be filtered and exported.
The camera can be moved in x, y and z direction (up and down as well as back and forth and vertically), to perfectly match the best depth of focus for each drop size. The solid system features height adjustable feet to compensate unevenness of the working surface.
* In a study (F. Bollon - Gattfossé, Let your hair down with a new texture, Personal Care Magazine, January 2022) a hair care emulsion was applied on a glass plate. After drying for 3 hours at 23°C and 30 % RH the hydrophobic properties of the active agent could be demonstrated by drop shape measurements.
Computer: Windows® 10, USB 2.0/3.0, computer specifications must meet system requirements (please ask for details).Technical changes may be made without prior notice.