Gardco PG-1 Посібник користувача - Сторінка 12

Переглянути онлайн або завантажити pdf Посібник користувача для Випробувальне обладнання Gardco PG-1. Gardco PG-1 17 сторінок. The pocket goniometer

3. Static and Dynamic Contact Angles

The terminology around contact angles can be slightly confusing.

It is therefore important to know the different types of contact angles, their applications and

how they are measured.

3.1 The Static Contact Angle

This contact angle is measured at "equilibrium" conditions and is only valid for solid, smooth

surfaces not penetrated by the test liquid. Section 4.1 contains a description on how to

measure the static contact angle at equilibrium with the PocketGoniometer model PG-1.

3.2 The Dynamic Contact Angle ("surface hysteresis")

The interaction between a liquid droplet and a specimen surface is not always characterised

by a single contact angle value. In fact, there is a range of contact angles that may appear as a

result. A higher contact angle may appear as the liquid advances across the dry surface. When

the liquid retracts from a wet surface, a lower contact angle may appear as the droplet is

receding. This type of dynamic contact angle is referred to as "surface hysteresis" described

by the advancing and receding contact angles. The purpose of this characterisation is to

determine the wetting/de-wetting characteristics of a surface. Section 4.2 describes how the

surface hysteresis is measured with the PocketGoniometer model PG-1.

3.3 The Dynamic Contact Angle ("function of time")

When the liquid spreads across or penetrates into the substrate, the contact angle will change

continuously. This "dynamic" contact angle is described as a function of time, where

requested data is reported at selected times. To test dynamic contact angles as a function of

time, it is necessary to capture a sequence of images with a video camera. The

PocketGoniometer model PG-2 and PG-3 have an integrated camera for automatic

determination of dynamic contact angles as a function of time.

The contact angle can be measured in different ways depending on the test application. This

Section describes the principal applications and how to perform these tests with your

PocketGoniometer model PG-1.

This approach is valid for smooth, solid surfaces where the test liquid does not penetrate into

the substrate. For liquids with high viscosity (e.g. glycerine) the contact angle reading is taken

when the liquid droplet is not spreading any further (at "equilibrium" conditions).

Cut a specimen as described in Section 5 and install it on the specimen stage as described

in Section 2.2. The specimen surface should be viewed slightly from above.

Fill the manual dispenser with the preferred test liquid as described in Section 2.3.

Insert the manual dispenser into the dispensing bridge.

Pump out a droplet of the requested size (Section 2.4).