Capillary forces are the cause of automatic penetration of liquid in fibrous network. Voids between fibers are assumed as capillary interstice which can be filled by liquid. The most important factors in capillary are surface area and void size, which vary in nanoyarns in comparison to normal yarns. Because, nanofibers and their produced yarns, have extended surface area and nanometer scale voides.This characteristic of fibers is very important in most of textile operations such as dyeing, printing, finishing and composites. This study is based on the observation and measurement of capillarity of colored liquid. For this reason, liquid height (h) is expressed as a function of time (t). During the capillary rising of colored liquid through the yarn, images taken by a digital camera should be analyzed. The height of liquid in different parts of cross section is not similar, due to the heterogeneous of yarn structure. So, the liquid surface should be measured in yarn cross section. For the capillary experiments, the produced yarn is a nonofiber. The polymer chosen for producing yarn is poly (acrylo nitrile). In optimizing conditions, the yarn is electrospun in three twist level of 1174, 1956 and 3639 TPM. Afterwards, heat setting has been done in boiling water, using tensile method. Yarns with 50% and 100% heatset and a kind of yarn without heat setting, are produce by this method. Yarns are maintained in standard condition of 65% relative humidity and 22 °C for 24 hours. The liquid used for capillary experiments and observation of penetrated water, is aquapura with 2% of detergent and 0.5% of acid dye. The rate of dye and water penetration in yarn structure is perceptible, as the chromatography can be seen for some yarns in final times of experiments. In this study the effect of yarn twist and heat setting on capillary rate coefficient is determined. The Lucas-wash burn equation is confirmed for all cases ( f(t) = h 2 =A.t ). In this equation the earth gravity is connivanced. Capillary rate coefficient is the curve slope of height square against time. Totally, capillary rate coefficient will reduce by increasing yarn twist, due to the reduction in capillary interstice size and unity of capillary. According to statistical results, twist level affect significantly the capillary rise of colored liquid in yarn.
